Schedule III - Real Estate and Accumulated Depreciation (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 Years
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	$ 512,391	[1]
Initial Cost
Land	666,690
Buildings and Improvements	3,603,754
Net Improvements (Retirements Since Acquistion)	522,640
Carrying Amount at Which Carried
Land	677,891
Buildings and Improvements	4,115,189
Total	4,793,080	[2]
Accumulated Depreciation at December 31, 2011	865,710	[3]
400 Berwyn Park [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,657
Buildings and Improvements	4,462
Net Improvements (Retirements Since Acquistion)	15,031
Carrying Amount at Which Carried
Land	2,657
Buildings and Improvements	19,493
Total	22,150	[2]
Accumulated Depreciation at December 31, 2011	6,742	[3]
Depreciable Life (Years)	40
300 Berwyn Park [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	9,971	[1]
Initial Cost
Land	2,206
Buildings and Improvements	13,422
Net Improvements (Retirements Since Acquistion)	4,161
Carrying Amount at Which Carried
Land	2,206
Buildings and Improvements	17,583
Total	19,789	[2]
Accumulated Depreciation at December 31, 2011	6,554	[3]
Depreciable Life (Years)	40
1200 Swedesford Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	1,887	[1]
Initial Cost
Land	2,595
Buildings and Improvements	11,809
Net Improvements (Retirements Since Acquistion)	3,778
Carrying Amount at Which Carried
Land	2,596
Buildings and Improvements	15,586
Total	18,182	[2]
Accumulated Depreciation at December 31, 2011	3,893	[3]
Depreciable Life (Years)	40
1050 Westlakes Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,611
Buildings and Improvements	10,445
Net Improvements (Retirements Since Acquistion)	5,046
Carrying Amount at Which Carried
Land	2,611
Buildings and Improvements	15,491
Total	18,102	[2]
Accumulated Depreciation at December 31, 2011	5,820	[3]
Depreciable Life (Years)	40
200 Berwyn Park [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	6,887	[1]
Initial Cost
Land	1,533
Buildings and Improvements	9,460
Net Improvements (Retirements Since Acquistion)	1,615
Carrying Amount at Which Carried
Land	1,533
Buildings and Improvements	11,075
Total	12,608	[2]
Accumulated Depreciation at December 31, 2011	4,512	[3]
Depreciable Life (Years)	40
1080 Swedesford Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,086
Buildings and Improvements	8,342
Net Improvements (Retirements Since Acquistion)	1,262
Carrying Amount at Which Carried
Land	2,085
Buildings and Improvements	9,605
Total	11,690	[2]
Accumulated Depreciation at December 31, 2011	3,198	[3]
Depreciable Life (Years)	40
100 Berwyn Park [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	5,299	[1]
Initial Cost
Land	1,180
Buildings and Improvements	7,290
Net Improvements (Retirements Since Acquistion)	2,144
Carrying Amount at Which Carried
Land	1,180
Buildings and Improvements	9,434
Total	10,614	[2]
Accumulated Depreciation at December 31, 2011	3,636	[3]
Depreciable Life (Years)	40
1160 Swedesford Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,781
Buildings and Improvements	7,124
Net Improvements (Retirements Since Acquistion)	1,071
Carrying Amount at Which Carried
Land	1,781
Buildings and Improvements	8,195
Total	9,976	[2]
Accumulated Depreciation at December 31, 2011	2,690	[3]
Depreciable Life (Years)	40
1100 Cassett Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,695
Buildings and Improvements	6,779
Net Improvements (Retirements Since Acquistion)	102
Carrying Amount at Which Carried
Land	1,694
Buildings and Improvements	6,882
Total	8,576	[2]
Accumulated Depreciation at December 31, 2011	1,823	[3]
Depreciable Life (Years)	40
980 Harvest Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	3,304
Buildings and Improvements	16,960
Net Improvements (Retirements Since Acquistion)	(808)
Carrying Amount at Which Carried
Land	3,304
Buildings and Improvements	16,152
Total	19,456	[2]
Accumulated Depreciation at December 31, 2011	5,167	[3]
Depreciable Life (Years)	40
925 Harvest Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,671
Buildings and Improvements	6,606
Net Improvements (Retirements Since Acquistion)	770
Carrying Amount at Which Carried
Land	1,670
Buildings and Improvements	7,377
Total	9,047	[2]
Accumulated Depreciation at December 31, 2011	2,837	[3]
Depreciable Life (Years)	40
920 Harvest Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,209
Buildings and Improvements	6,595
Net Improvements (Retirements Since Acquistion)	(125)
Carrying Amount at Which Carried
Land	1,208
Buildings and Improvements	6,471
Total	7,679	[2]
Accumulated Depreciation at December 31, 2011	3,088	[3]
Depreciable Life (Years)	40
426 Lancaster Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,689
Buildings and Improvements	6,756
Net Improvements (Retirements Since Acquistion)	405
Carrying Amount at Which Carried
Land	1,688
Buildings and Improvements	7,162
Total	8,850	[2]
Accumulated Depreciation at December 31, 2011	2,884	[3]
Depreciable Life (Years)	40
52 Swedesford Square [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	4,241
Buildings and Improvements	16,579
Net Improvements (Retirements Since Acquistion)	557
Carrying Amount at Which Carried
Land	4,241
Buildings and Improvements	17,136
Total	21,377	[2]
Accumulated Depreciation at December 31, 2011	6,341	[3]
Depreciable Life (Years)	40
429 Creamery Way [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,368
Buildings and Improvements	5,471
Net Improvements (Retirements Since Acquistion)	451
Carrying Amount at Which Carried
Land	1,368
Buildings and Improvements	5,922
Total	7,290	[2]
Accumulated Depreciation at December 31, 2011	1,667	[3]
Depreciable Life (Years)	40
412 Creamery Way [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,195
Buildings and Improvements	4,779
Net Improvements (Retirements Since Acquistion)	1,123
Carrying Amount at Which Carried
Land	1,195
Buildings and Improvements	5,902
Total	7,097	[2]
Accumulated Depreciation at December 31, 2011	1,612	[3]
Depreciable Life (Years)	40
440 Creamery Way [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	982
Buildings and Improvements	3,927
Net Improvements (Retirements Since Acquistion)	1,900
Carrying Amount at Which Carried
Land	982
Buildings and Improvements	5,827
Total	6,809	[2]
Accumulated Depreciation at December 31, 2011	2,124	[3]
Depreciable Life (Years)	40
436 Creamery Way [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	994
Buildings and Improvements	3,978
Net Improvements (Retirements Since Acquistion)	686
Carrying Amount at Which Carried
Land	994
Buildings and Improvements	4,664
Total	5,658	[2]
Accumulated Depreciation at December 31, 2011	1,251	[3]
Depreciable Life (Years)	40
467 Creamery Way [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	906
Buildings and Improvements	3,623
Net Improvements (Retirements Since Acquistion)	1,070
Carrying Amount at Which Carried
Land	906
Buildings and Improvements	4,693
Total	5,599	[2]
Accumulated Depreciation at December 31, 2011	1,353	[3]
Depreciable Life (Years)	40
100 Arrandale Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	970
Buildings and Improvements	3,878
Net Improvements (Retirements Since Acquistion)	274
Carrying Amount at Which Carried
Land	970
Buildings and Improvements	4,152
Total	5,122	[2]
Accumulated Depreciation at December 31, 2011	1,275	[3]
Depreciable Life (Years)	40
457 Creamery Way [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	777
Buildings and Improvements	3,107
Net Improvements (Retirements Since Acquistion)	1,035
Carrying Amount at Which Carried
Land	777
Buildings and Improvements	4,142
Total	4,919	[2]
Accumulated Depreciation at December 31, 2011	1,062	[3]
Depreciable Life (Years)	40
486 Thomas Jones Way [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	806
Buildings and Improvements	3,256
Net Improvements (Retirements Since Acquistion)	605
Carrying Amount at Which Carried
Land	806
Buildings and Improvements	3,861
Total	4,667	[2]
Accumulated Depreciation at December 31, 2011	1,710	[3]
Depreciable Life (Years)	40
468 Thomas Jones Way [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	526
Buildings and Improvements	2,112
Net Improvements (Retirements Since Acquistion)	612
Carrying Amount at Which Carried
Land	526
Buildings and Improvements	2,724
Total	3,250	[2]
Accumulated Depreciation at December 31, 2011	972	[3]
Depreciable Life (Years)	40
456 Creamery Way [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	635
Buildings and Improvements	2,548
Net Improvements (Retirements Since Acquistion)	(48)
Carrying Amount at Which Carried
Land	636
Buildings and Improvements	2,499
Total	3,135	[2]
Accumulated Depreciation at December 31, 2011	1,135	[3]
Depreciable Life (Years)	40
481 John Young Way [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	496
Buildings and Improvements	1,983
Net Improvements (Retirements Since Acquistion)	14
Carrying Amount at Which Carried
Land	496
Buildings and Improvements	1,997
Total	2,493	[2]
Accumulated Depreciation at December 31, 2011	540	[3]
Depreciable Life (Years)	40
111 Arrandale Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	262
Buildings and Improvements	1,048
Net Improvements (Retirements Since Acquistion)	125
Carrying Amount at Which Carried
Land	262
Buildings and Improvements	1,173
Total	1,435	[2]
Accumulated Depreciation at December 31, 2011	404	[3]
Depreciable Life (Years)	40
One Progress Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,399
Buildings and Improvements	5,629
Net Improvements (Retirements Since Acquistion)	4,466
Carrying Amount at Which Carried
Land	1,399
Buildings and Improvements	10,095
Total	11,494	[2]
Accumulated Depreciation at December 31, 2011	2,777	[3]
Depreciable Life (Years)	40
500 Enterprise Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,303
Buildings and Improvements	5,188
Net Improvements (Retirements Since Acquistion)	3,228
Carrying Amount at Which Carried
Land	1,303
Buildings and Improvements	8,416
Total	9,719	[2]
Accumulated Depreciation at December 31, 2011	2,566	[3]
Depreciable Life (Years)	40
640 Freedom Business Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	4,222
Buildings and Improvements	16,891
Net Improvements (Retirements Since Acquistion)	2,964
Carrying Amount at Which Carried
Land	4,222
Buildings and Improvements	19,855
Total	24,077	[2]
Accumulated Depreciation at December 31, 2011	7,867	[3]
Depreciable Life (Years)	40
555 Croton Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	4,486
Buildings and Improvements	17,943
Net Improvements (Retirements Since Acquistion)	1,215
Carrying Amount at Which Carried
Land	4,486
Buildings and Improvements	19,158
Total	23,644	[2]
Accumulated Depreciation at December 31, 2011	5,461	[3]
Depreciable Life (Years)	40
630 Allendale Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,836
Buildings and Improvements	4,028
Net Improvements (Retirements Since Acquistion)	12,275
Carrying Amount at Which Carried
Land	2,636
Buildings and Improvements	16,503
Total	19,139	[2]
Accumulated Depreciation at December 31, 2011	4,385	[3]
Depreciable Life (Years)	40
1000 First Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,772
Buildings and Improvements	10,936
Net Improvements (Retirements Since Acquistion)	3,524
Carrying Amount at Which Carried
Land	2,772
Buildings and Improvements	14,460
Total	17,232	[2]
Accumulated Depreciation at December 31, 2011	5,838	[3]
Depreciable Life (Years)	40
620 Freedom Business Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,770
Buildings and Improvements	11,014
Net Improvements (Retirements Since Acquistion)	3,413
Carrying Amount at Which Carried
Land	2,769
Buildings and Improvements	14,428
Total	17,197	[2]
Accumulated Depreciation at December 31, 2011	6,184	[3]
Depreciable Life (Years)	40
1060 First Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,712
Buildings and Improvements	10,953
Net Improvements (Retirements Since Acquistion)	2,378
Carrying Amount at Which Carried
Land	2,712
Buildings and Improvements	13,331
Total	16,043	[2]
Accumulated Depreciation at December 31, 2011	5,006	[3]
Depreciable Life (Years)	40
1040 First Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,860
Buildings and Improvements	11,282
Net Improvements (Retirements Since Acquistion)	1,303
Carrying Amount at Which Carried
Land	2,860
Buildings and Improvements	12,585
Total	15,445	[2]
Accumulated Depreciation at December 31, 2011	4,717	[3]
Depreciable Life (Years)	40
630 Freedom Business Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,773
Buildings and Improvements	11,144
Net Improvements (Retirements Since Acquistion)	1,199
Carrying Amount at Which Carried
Land	2,773
Buildings and Improvements	12,343
Total	15,116	[2]
Accumulated Depreciation at December 31, 2011	4,910	[3]
Depreciable Life (Years)	40
1020 First Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,168
Buildings and Improvements	8,576
Net Improvements (Retirements Since Acquistion)	4,117
Carrying Amount at Which Carried
Land	2,168
Buildings and Improvements	12,693
Total	14,861	[2]
Accumulated Depreciation at December 31, 2011	5,079	[3]
Depreciable Life (Years)	40
610 Freedom Business Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,017
Buildings and Improvements	8,070
Net Improvements (Retirements Since Acquistion)	1,195
Carrying Amount at Which Carried
Land	2,017
Buildings and Improvements	9,265
Total	11,282	[2]
Accumulated Depreciation at December 31, 2011	3,546	[3]
Depreciable Life (Years)	40
500 North Gulph Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,303
Buildings and Improvements	5,201
Net Improvements (Retirements Since Acquistion)	1,834
Carrying Amount at Which Carried
Land	1,303
Buildings and Improvements	7,035
Total	8,338	[2]
Accumulated Depreciation at December 31, 2011	2,988	[3]
Depreciable Life (Years)	40
650 Park Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,916
Buildings and Improvements	4,378
Net Improvements (Retirements Since Acquistion)	2,042
Carrying Amount at Which Carried
Land	1,917
Buildings and Improvements	6,419
Total	8,336	[2]
Accumulated Depreciation at December 31, 2011	2,819	[3]
Depreciable Life (Years)	40
741 First Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,287
Buildings and Improvements	5,151
Net Improvements (Retirements Since Acquistion)	12
Carrying Amount at Which Carried
Land	1,288
Buildings and Improvements	5,162
Total	6,450	[2]
Accumulated Depreciation at December 31, 2011	1,996	[3]
Depreciable Life (Years)	40
875 First Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	618
Buildings and Improvements	2,473
Net Improvements (Retirements Since Acquistion)	3,239
Carrying Amount at Which Carried
Land	618
Buildings and Improvements	5,712
Total	6,330	[2]
Accumulated Depreciation at December 31, 2011	2,438	[3]
Depreciable Life (Years)	40
751-761 Fifth Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,097
Buildings and Improvements	4,391
Net Improvements (Retirements Since Acquistion)	31
Carrying Amount at Which Carried
Land	1,097
Buildings and Improvements	4,422
Total	5,519	[2]
Accumulated Depreciation at December 31, 2011	1,712	[3]
Depreciable Life (Years)	40
600 Park Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,012
Buildings and Improvements	4,048
Net Improvements (Retirements Since Acquistion)	385
Carrying Amount at Which Carried
Land	1,012
Buildings and Improvements	4,433
Total	5,445	[2]
Accumulated Depreciation at December 31, 2011	1,684	[3]
Depreciable Life (Years)	40
620 Allendale Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,020
Buildings and Improvements	3,839
Net Improvements (Retirements Since Acquistion)	503
Carrying Amount at Which Carried
Land	1,020
Buildings and Improvements	4,342
Total	5,362	[2]
Accumulated Depreciation at December 31, 2011	1,645	[3]
Depreciable Life (Years)	40
660 Allendale Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	396
Buildings and Improvements	948
Net Improvements (Retirements Since Acquistion)	2,505
Carrying Amount at Which Carried
Land	1,085
Buildings and Improvements	2,764
Total	3,849	[2]
Accumulated Depreciation at December 31, 2011	42	[3]
Depreciable Life (Years)	40
640 Allendale Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	439
Buildings and Improvements	432
Net Improvements (Retirements Since Acquistion)	1,553
Carrying Amount at Which Carried
Land	439
Buildings and Improvements	1,985
Total	2,424	[2]
Accumulated Depreciation at December 31, 2011	564	[3]
Depreciable Life (Years)	40
101 Lindenwood Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	4,152
Buildings and Improvements	16,606
Net Improvements (Retirements Since Acquistion)	3,331
Carrying Amount at Which Carried
Land	4,152
Buildings and Improvements	19,937
Total	24,089	[2]
Accumulated Depreciation at December 31, 2011	4,954	[3]
Depreciable Life (Years)	40
301 Lindenwood Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,729
Buildings and Improvements	10,915
Net Improvements (Retirements Since Acquistion)	1,264
Carrying Amount at Which Carried
Land	2,729
Buildings and Improvements	12,179
Total	14,908	[2]
Accumulated Depreciation at December 31, 2011	3,541	[3]
Depreciable Life (Years)	40
300 Lindenwood Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	848
Buildings and Improvements	3,394
Net Improvements (Retirements Since Acquistion)	1,334
Carrying Amount at Which Carried
Land	849
Buildings and Improvements	4,727
Total	5,576	[2]
Accumulated Depreciation at December 31, 2011	1,532	[3]
Depreciable Life (Years)	40
1700 Paoli Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	458
Buildings and Improvements	559
Net Improvements (Retirements Since Acquistion)	3,018
Carrying Amount at Which Carried
Land	488
Buildings and Improvements	3,547
Total	4,035	[2]
Accumulated Depreciation at December 31, 2011	977	[3]
Depreciable Life (Years)	40
100 Lindenwood Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	473
Buildings and Improvements	1,892
Net Improvements (Retirements Since Acquistion)	188
Carrying Amount at Which Carried
Land	474
Buildings and Improvements	2,079
Total	2,553	[2]
Accumulated Depreciation at December 31, 2011	575	[3]
Depreciable Life (Years)	40
200 Lindenwood Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	324
Buildings and Improvements	1,295
Net Improvements (Retirements Since Acquistion)	335
Carrying Amount at Which Carried
Land	324
Buildings and Improvements	1,630
Total	1,954	[2]
Accumulated Depreciation at December 31, 2011	378	[3]
Depreciable Life (Years)	40
14 Campus Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	6,384	[1]
Initial Cost
Land	2,244
Buildings and Improvements	4,217
Net Improvements (Retirements Since Acquistion)	1,515
Carrying Amount at Which Carried
Land	2,243
Buildings and Improvements	5,733
Total	7,976	[2]
Accumulated Depreciation at December 31, 2011	2,311	[3]
Depreciable Life (Years)	40
11 Campus Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	4,379	[1]
Initial Cost
Land	1,112
Buildings and Improvements	4,067
Net Improvements (Retirements Since Acquistion)	1,047
Carrying Amount at Which Carried
Land	1,112
Buildings and Improvements	5,114
Total	6,226	[2]
Accumulated Depreciation at December 31, 2011	1,836	[3]
Depreciable Life (Years)	40
17 Campus Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	4,458	[1]
Initial Cost
Land	1,108
Buildings and Improvements	5,155
Net Improvements (Retirements Since Acquistion)	(397)
Carrying Amount at Which Carried
Land	1,108
Buildings and Improvements	4,758
Total	5,866	[2]
Accumulated Depreciation at December 31, 2011	1,098	[3]
Depreciable Life (Years)	40
15 Campus Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	4,555	[1]
Initial Cost
Land	1,164
Buildings and Improvements	3,896
Net Improvements (Retirements Since Acquistion)	229
Carrying Amount at Which Carried
Land	1,164
Buildings and Improvements	4,125
Total	5,289	[2]
Accumulated Depreciation at December 31, 2011	1,016	[3]
Depreciable Life (Years)	40
18 Campus Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	3,431	[1]
Initial Cost
Land	787
Buildings and Improvements	3,312
Net Improvements (Retirements Since Acquistion)	313
Carrying Amount at Which Carried
Land	787
Buildings and Improvements	3,625
Total	4,412	[2]
Accumulated Depreciation at December 31, 2011	1,780	[3]
Depreciable Life (Years)	40
401 Plymouth Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	6,198
Buildings and Improvements	16,131
Net Improvements (Retirements Since Acquistion)	15,959
Carrying Amount at Which Carried
Land	6,199
Buildings and Improvements	32,089
Total	38,288	[2]
Accumulated Depreciation at December 31, 2011	8,130	[3]
Depreciable Life (Years)	40
4000 Chemical Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	4,373
Buildings and Improvements	24,546
Net Improvements (Retirements Since Acquistion)	4,509
Carrying Amount at Which Carried
Land	4,373
Buildings and Improvements	29,055
Total	33,428	[2]
Accumulated Depreciation at December 31, 2011	4,005	[3]
Depreciable Life (Years)	40
610 West Germantown Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	3,651
Buildings and Improvements	14,514
Net Improvements (Retirements Since Acquistion)	3,017
Carrying Amount at Which Carried
Land	3,651
Buildings and Improvements	17,531
Total	21,182	[2]
Accumulated Depreciation at December 31, 2011	4,595	[3]
Depreciable Life (Years)	40
600 West Germantown Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	3,652
Buildings and Improvements	15,288
Net Improvements (Retirements Since Acquistion)	1,958
Carrying Amount at Which Carried
Land	3,652
Buildings and Improvements	17,246
Total	20,898	[2]
Accumulated Depreciation at December 31, 2011	4,225	[3]
Depreciable Life (Years)	40
630 West Germantown Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	3,558
Buildings and Improvements	14,743
Net Improvements (Retirements Since Acquistion)	2,199
Carrying Amount at Which Carried
Land	3,558
Buildings and Improvements	16,942
Total	20,500	[2]
Accumulated Depreciation at December 31, 2011	4,585	[3]
Depreciable Life (Years)	40
620 West Germantown Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	3,572
Buildings and Improvements	14,435
Net Improvements (Retirements Since Acquistion)	1,220
Carrying Amount at Which Carried
Land	3,572
Buildings and Improvements	15,655
Total	19,227	[2]
Accumulated Depreciation at December 31, 2011	3,921	[3]
Depreciable Life (Years)	40
2240/2250 Butler Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,104
Buildings and Improvements	4,627
Net Improvements (Retirements Since Acquistion)	1,277
Carrying Amount at Which Carried
Land	1,104
Buildings and Improvements	5,904
Total	7,008	[2]
Accumulated Depreciation at December 31, 2011	2,929	[3]
Depreciable Life (Years)	40
2260 Butler Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	661
Buildings and Improvements	2,727
Net Improvements (Retirements Since Acquistion)	1,198
Carrying Amount at Which Carried
Land	662
Buildings and Improvements	3,924
Total	4,586	[2]
Accumulated Depreciation at December 31, 2011	1,710	[3]
Depreciable Life (Years)	40
120 West Germantown Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	685
Buildings and Improvements	2,773
Net Improvements (Retirements Since Acquistion)	631
Carrying Amount at Which Carried
Land	685
Buildings and Improvements	3,404
Total	4,089	[2]
Accumulated Depreciation at December 31, 2011	1,481	[3]
Depreciable Life (Years)	40
140 West Germantown Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	481
Buildings and Improvements	1,976
Net Improvements (Retirements Since Acquistion)	318
Carrying Amount at Which Carried
Land	481
Buildings and Improvements	2,294
Total	2,775	[2]
Accumulated Depreciation at December 31, 2011	1,096	[3]
Depreciable Life (Years)	40
351 Plymouth Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,043
Buildings and Improvements	555
Net Improvements (Retirements Since Acquistion)	0
Carrying Amount at Which Carried
Land	1,043
Buildings and Improvements	555
Total	1,598	[2]
Accumulated Depreciation at December 31, 2011	94	[3]
Depreciable Life (Years)	40
150 Radnor Chester Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	11,925
Buildings and Improvements	36,986
Net Improvements (Retirements Since Acquistion)	12,838
Carrying Amount at Which Carried
Land	11,897
Buildings and Improvements	49,852
Total	61,749	[2]
Accumulated Depreciation at December 31, 2011	12,855	[3]
Depreciable Life (Years)	29
One Radnor Corporate Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	7,323
Buildings and Improvements	28,613
Net Improvements (Retirements Since Acquistion)	22,241
Carrying Amount at Which Carried
Land	7,323
Buildings and Improvements	50,854
Total	58,177	[2]
Accumulated Depreciation at December 31, 2011	10,296	[3]
Depreciable Life (Years)	29
201 King of Prussia Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	8,956
Buildings and Improvements	29,811
Net Improvements (Retirements Since Acquistion)	6,700
Carrying Amount at Which Carried
Land	8,949
Buildings and Improvements	36,518
Total	45,467	[2]
Accumulated Depreciation at December 31, 2011	11,783	[3]
Depreciable Life (Years)	25
555 Lancaster Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	8,014
Buildings and Improvements	16,508
Net Improvements (Retirements Since Acquistion)	18,711
Carrying Amount at Which Carried
Land	8,609
Buildings and Improvements	34,624
Total	43,233	[2]
Accumulated Depreciation at December 31, 2011	9,207	[3]
Depreciable Life (Years)	24
Four Radnor Corporate Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	5,406
Buildings and Improvements	21,390
Net Improvements (Retirements Since Acquistion)	11,350
Carrying Amount at Which Carried
Land	5,705
Buildings and Improvements	32,441
Total	38,146	[2]
Accumulated Depreciation at December 31, 2011	9,291	[3]
Depreciable Life (Years)	30
Five Radnor Corporate Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	6,506
Buildings and Improvements	25,525
Net Improvements (Retirements Since Acquistion)	2,159
Carrying Amount at Which Carried
Land	6,578
Buildings and Improvements	27,612
Total	34,190	[2]
Accumulated Depreciation at December 31, 2011	6,414	[3]
Depreciable Life (Years)	38
Three Radnor Corporate Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	4,773
Buildings and Improvements	17,961
Net Improvements (Retirements Since Acquistion)	2,361
Carrying Amount at Which Carried
Land	4,792
Buildings and Improvements	20,303
Total	25,095	[2]
Accumulated Depreciation at December 31, 2011	5,259	[3]
Depreciable Life (Years)	29
Two Radnor Corporate Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	3,937
Buildings and Improvements	15,484
Net Improvements (Retirements Since Acquistion)	1,208
Carrying Amount at Which Carried
Land	3,942
Buildings and Improvements	16,687
Total	20,629	[2]
Accumulated Depreciation at December 31, 2011	4,396	[3]
Depreciable Life (Years)	29
130 Radnor Chester Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,573
Buildings and Improvements	8,338
Net Improvements (Retirements Since Acquistion)	3,542
Carrying Amount at Which Carried
Land	2,568
Buildings and Improvements	11,885
Total	14,453	[2]
Accumulated Depreciation at December 31, 2011	2,788	[3]
Depreciable Life (Years)	25
170 Radnor Chester Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,514
Buildings and Improvements	8,147
Net Improvements (Retirements Since Acquistion)	3,283
Carrying Amount at Which Carried
Land	2,508
Buildings and Improvements	11,436
Total	13,944	[2]
Accumulated Depreciation at December 31, 2011	3,203	[3]
Depreciable Life (Years)	25
101 West Elm Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	6,251
Buildings and Improvements	25,209
Net Improvements (Retirements Since Acquistion)	3,010
Carrying Amount at Which Carried
Land	6,252
Buildings and Improvements	28,218
Total	34,470	[2]
Accumulated Depreciation at December 31, 2011	4,845	[3]
Depreciable Life (Years)	40
1 West Elm Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	3,557
Buildings and Improvements	14,249
Net Improvements (Retirements Since Acquistion)	1,128
Carrying Amount at Which Carried
Land	3,557
Buildings and Improvements	15,377
Total	18,934	[2]
Accumulated Depreciation at December 31, 2011	2,497	[3]
Depreciable Life (Years)	40
595 East Swedesford Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,729
Buildings and Improvements	10,917
Net Improvements (Retirements Since Acquistion)	2,072
Carrying Amount at Which Carried
Land	2,729
Buildings and Improvements	12,989
Total	15,718	[2]
Accumulated Depreciation at December 31, 2011	2,939	[3]
Depreciable Life (Years)	40
575 East Swedesford Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,178
Buildings and Improvements	8,712
Net Improvements (Retirements Since Acquistion)	1,630
Carrying Amount at Which Carried
Land	2,178
Buildings and Improvements	10,342
Total	12,520	[2]
Accumulated Depreciation at December 31, 2011	2,551	[3]
Depreciable Life (Years)	40
565 East Swedesford Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,872
Buildings and Improvements	7,489
Net Improvements (Retirements Since Acquistion)	1,785
Carrying Amount at Which Carried
Land	1,872
Buildings and Improvements	9,274
Total	11,146	[2]
Accumulated Depreciation at December 31, 2011	2,208	[3]
Depreciable Life (Years)	40
585 East Swedesford Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,350
Buildings and Improvements	5,401
Net Improvements (Retirements Since Acquistion)	358
Carrying Amount at Which Carried
Land	1,351
Buildings and Improvements	5,758
Total	7,109	[2]
Accumulated Depreciation at December 31, 2011	1,325	[3]
Depreciable Life (Years)	40
1336 Enterprise Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	731
Buildings and Improvements	2,946
Net Improvements (Retirements Since Acquistion)	47
Carrying Amount at Which Carried
Land	731
Buildings and Improvements	2,993
Total	3,724	[2]
Accumulated Depreciation at December 31, 2011	1,275	[3]
Depreciable Life (Years)	40
2970 Market Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	202,905	[1]
Initial Cost
Land	22,430
Buildings and Improvements	217,763
Net Improvements (Retirements Since Acquistion)	9,956
Carrying Amount at Which Carried
Land	22,430
Buildings and Improvements	227,719
Total	250,149	[2]
Accumulated Depreciation at December 31, 2011	8,408	[3]
Depreciable Life (Years)	40
2929 Arch Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	0
Buildings and Improvements	208,570
Net Improvements (Retirements Since Acquistion)	18,366
Carrying Amount at Which Carried
Land	0
Buildings and Improvements	226,936
Total	226,936	[2]
Accumulated Depreciation at December 31, 2011	55,716	[3]
Depreciable Life (Years)	40
130 North 18th Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	14,496
Buildings and Improvements	107,736
Net Improvements (Retirements Since Acquistion)	10,054
Carrying Amount at Which Carried
Land	14,473
Buildings and Improvements	117,813
Total	132,286	[2]
Accumulated Depreciation at December 31, 2011	28,639	[3]
Depreciable Life (Years)	23
100 North 18th Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	89,800	[1]
Initial Cost
Land	16,066
Buildings and Improvements	100,255
Net Improvements (Retirements Since Acquistion)	5,671
Carrying Amount at Which Carried
Land	16,066
Buildings and Improvements	105,926
Total	121,992	[2]
Accumulated Depreciation at December 31, 2011	26,011	[3]
Depreciable Life (Years)	33
1717 Arch Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	0
Buildings and Improvements	98,188
Net Improvements (Retirements Since Acquistion)	3,346
Carrying Amount at Which Carried
Land	0
Buildings and Improvements	101,534
Total	101,534	[2]
Accumulated Depreciation at December 31, 2011	7,383	[3]
Depreciable Life (Years)	40
2930 Chestnut Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	44,379	[1]
Initial Cost
Land	0
Buildings and Improvements	76,008
Net Improvements (Retirements Since Acquistion)	3,064
Carrying Amount at Which Carried
Land	0
Buildings and Improvements	79,072
Total	79,072	[2]
Accumulated Depreciation at December 31, 2011	2,600	[3]
Depreciable Life (Years)	40
3020 Market Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	0
Buildings and Improvements	21,417
Net Improvements (Retirements Since Acquistion)	20
Carrying Amount at Which Carried
Land	0
Buildings and Improvements	21,437
Total	21,437	[2]
Accumulated Depreciation at December 31, 2011	277	[3]
Depreciable Life (Years)	26
101-103 Juniper Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	0
Buildings and Improvements	14,401
Net Improvements (Retirements Since Acquistion)	76
Carrying Amount at Which Carried
Land	0
Buildings and Improvements	14,477
Total	14,477	[2]
Accumulated Depreciation at December 31, 2011	212	[3]
Depreciable Life (Years)	40
Philadelphia Marine Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	532
Buildings and Improvements	2,196
Net Improvements (Retirements Since Acquistion)	3,236
Carrying Amount at Which Carried
Land	628
Buildings and Improvements	5,336
Total	5,964	[2]
Accumulated Depreciation at December 31, 2011	1,749	[3]
Depreciable Life (Years)	40
11720 Beltsville Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	3,831
Buildings and Improvements	16,661
Net Improvements (Retirements Since Acquistion)	4,047
Carrying Amount at Which Carried
Land	3,903
Buildings and Improvements	20,636
Total	24,539	[2]
Accumulated Depreciation at December 31, 2011	4,357	[3]
Depreciable Life (Years)	46
11700 Beltsville Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,808
Buildings and Improvements	12,081
Net Improvements (Retirements Since Acquistion)	339
Carrying Amount at Which Carried
Land	2,863
Buildings and Improvements	12,365
Total	15,228	[2]
Accumulated Depreciation at December 31, 2011	2,033	[3]
Depreciable Life (Years)	46
11710 Beltsville Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,278
Buildings and Improvements	11,100
Net Improvements (Retirements Since Acquistion)	(769)
Carrying Amount at Which Carried
Land	2,322
Buildings and Improvements	10,288
Total	12,610	[2]
Accumulated Depreciation at December 31, 2011	1,578	[3]
Depreciable Life (Years)	46
6600 Rockledge Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	0
Buildings and Improvements	37,421
Net Improvements (Retirements Since Acquistion)	11,145
Carrying Amount at Which Carried
Land	0
Buildings and Improvements	48,566
Total	48,566	[2]
Accumulated Depreciation at December 31, 2011	8,529	[3]
Depreciable Life (Years)	50
11740 Beltsville Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	198
Buildings and Improvements	870
Net Improvements (Retirements Since Acquistion)	42
Carrying Amount at Which Carried
Land	203
Buildings and Improvements	908
Total	1,111	[2]
Accumulated Depreciation at December 31, 2011	146	[3]
Depreciable Life (Years)	46
12015 Lee Jackson Memorial Highway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	3,770
Buildings and Improvements	22,895
Net Improvements (Retirements Since Acquistion)	2,702
Carrying Amount at Which Carried
Land	3,841
Buildings and Improvements	25,526
Total	29,367	[2]
Accumulated Depreciation at December 31, 2011	3,937	[3]
Depreciable Life (Years)	42
11781 Lee Jackson Memorial Highway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	3,246
Buildings and Improvements	19,836
Net Improvements (Retirements Since Acquistion)	(289)
Carrying Amount at Which Carried
Land	3,307
Buildings and Improvements	19,487
Total	22,794	[2]
Accumulated Depreciation at December 31, 2011	3,572	[3]
Depreciable Life (Years)	40
4401 Fair Lakes Court [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,569
Buildings and Improvements	11,982
Net Improvements (Retirements Since Acquistion)	284
Carrying Amount at Which Carried
Land	1,600
Buildings and Improvements	12,236
Total	13,836	[2]
Accumulated Depreciation at December 31, 2011	1,738	[3]
Depreciable Life (Years)	52
3141 Fairview Park Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	22,000	[1],[4]
Initial Cost
Land	5,918	[4]
Buildings and Improvements	40,981	[4]
Net Improvements (Retirements Since Acquistion)	8,917	[4]
Carrying Amount at Which Carried
Land	7,081	[4]
Buildings and Improvements	48,736	[4]
Total	55,817	[2],[4]
Accumulated Depreciation at December 31, 2011	6,499	[3],[4]
Depreciable Life (Years)	51	[4]
2340 Dulles Corner Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	16,345
Buildings and Improvements	65,379
Net Improvements (Retirements Since Acquistion)	18,370
Carrying Amount at Which Carried
Land	16,129
Buildings and Improvements	83,965
Total	100,094	[2]
Accumulated Depreciation at December 31, 2011	17,616	[3]
Depreciable Life (Years)	40
13820 Sunrise Valley Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	11,082
Buildings and Improvements	47,290
Net Improvements (Retirements Since Acquistion)	19,687
Carrying Amount at Which Carried
Land	11,082
Buildings and Improvements	66,977
Total	78,059	[2]
Accumulated Depreciation at December 31, 2011	8,334	[3]
Depreciable Life (Years)	40
2291 Wood Oak Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	8,243
Buildings and Improvements	52,413
Net Improvements (Retirements Since Acquistion)	12,805
Carrying Amount at Which Carried
Land	8,781
Buildings and Improvements	64,680
Total	73,461	[2]
Accumulated Depreciation at December 31, 2011	6,930	[3]
Depreciable Life (Years)	55
2355 Dulles Corner Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	10,365
Buildings and Improvements	43,876
Net Improvements (Retirements Since Acquistion)	4,418
Carrying Amount at Which Carried
Land	10,364
Buildings and Improvements	48,295
Total	58,659	[2]
Accumulated Depreciation at December 31, 2011	7,804	[3]
Depreciable Life (Years)	40
196/198 Van Buren Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	7,931
Buildings and Improvements	43,812
Net Improvements (Retirements Since Acquistion)	6,058
Carrying Amount at Which Carried
Land	8,348
Buildings and Improvements	49,453
Total	57,801	[2]
Accumulated Depreciation at December 31, 2011	7,660	[3]
Depreciable Life (Years)	53
2251 Corporate Park Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	11,472
Buildings and Improvements	45,893
Net Improvements (Retirements Since Acquistion)	337
Carrying Amount at Which Carried
Land	11,471
Buildings and Improvements	46,231
Total	57,702	[2]
Accumulated Depreciation at December 31, 2011	5,942	[3]
Depreciable Life (Years)	40
2411 Dulles Corner Park [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	7,279
Buildings and Improvements	46,340
Net Improvements (Retirements Since Acquistion)	3,691
Carrying Amount at Which Carried
Land	7,416
Buildings and Improvements	49,894
Total	57,310	[2]
Accumulated Depreciation at December 31, 2011	7,736	[3]
Depreciable Life (Years)	50
2121 Cooperative Way [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	5,598
Buildings and Improvements	38,639
Net Improvements (Retirements Since Acquistion)	1,330
Carrying Amount at Which Carried
Land	5,794
Buildings and Improvements	39,772
Total	45,566	[2]
Accumulated Depreciation at December 31, 2011	4,593	[3]
Depreciable Life (Years)	54
13880 Dulles Corner Lane [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	7,236
Buildings and Improvements	39,213
Net Improvements (Retirements Since Acquistion)	(1,132)
Carrying Amount at Which Carried
Land	7,373
Buildings and Improvements	37,943
Total	45,316	[2]
Accumulated Depreciation at December 31, 2011	4,816	[3]
Depreciable Life (Years)	55
2201 Cooperative Way [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	4,809
Buildings and Improvements	34,093
Net Improvements (Retirements Since Acquistion)	(678)
Carrying Amount at Which Carried
Land	4,809
Buildings and Improvements	33,416
Total	38,225	[2]
Accumulated Depreciation at December 31, 2011	3,936	[3]
Depreciable Life (Years)	54
13825 Sunrise Valley Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	3,794
Buildings and Improvements	19,365
Net Improvements (Retirements Since Acquistion)	(851)
Carrying Amount at Which Carried
Land	3,865
Buildings and Improvements	18,443
Total	22,308	[2]
Accumulated Depreciation at December 31, 2011	2,480	[3]
Depreciable Life (Years)	46
1676 International Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	61,976	[1]
Initial Cost
Land	18,437
Buildings and Improvements	97,538
Net Improvements (Retirements Since Acquistion)	1,650
Carrying Amount at Which Carried
Land	18,785
Buildings and Improvements	98,840
Total	117,625	[2]
Accumulated Depreciation at December 31, 2011	13,100	[3]
Depreciable Life (Years)	55
8260 Greensboro Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	32,906	[1]
Initial Cost
Land	7,952
Buildings and Improvements	33,964
Net Improvements (Retirements Since Acquistion)	242
Carrying Amount at Which Carried
Land	8,103
Buildings and Improvements	34,055
Total	42,158	[2]
Accumulated Depreciation at December 31, 2011	4,509	[3]
Depreciable Life (Years)	52
1880 Campus Commons Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	6,164
Buildings and Improvements	28,114
Net Improvements (Retirements Since Acquistion)	1,714
Carrying Amount at Which Carried
Land	6,281
Buildings and Improvements	29,711
Total	35,992	[2]
Accumulated Depreciation at December 31, 2011	3,636	[3]
Depreciable Life (Years)	52
2273 Research Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	5,167
Buildings and Improvements	31,110
Net Improvements (Retirements Since Acquistion)	3,179
Carrying Amount at Which Carried
Land	5,237
Buildings and Improvements	34,219
Total	39,456	[2]
Accumulated Depreciation at December 31, 2011	6,197	[3]
Depreciable Life (Years)	45
2275 Research Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	5,059
Buildings and Improvements	29,668
Net Improvements (Retirements Since Acquistion)	2,372
Carrying Amount at Which Carried
Land	5,154
Buildings and Improvements	31,945
Total	37,099	[2]
Accumulated Depreciation at December 31, 2011	5,358	[3]
Depreciable Life (Years)	45
2277 Research Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	4,649
Buildings and Improvements	26,952
Net Improvements (Retirements Since Acquistion)	823
Carrying Amount at Which Carried
Land	4,733
Buildings and Improvements	27,690
Total	32,423	[2]
Accumulated Depreciation at December 31, 2011	4,304	[3]
Depreciable Life (Years)	45
1900 Gallows Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	7,797
Buildings and Improvements	47,817
Net Improvements (Retirements Since Acquistion)	2,978
Carrying Amount at Which Carried
Land	7,944
Buildings and Improvements	50,648
Total	58,592	[2]
Accumulated Depreciation at December 31, 2011	6,300	[3]
Depreciable Life (Years)	52
8521 Leesburg Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	4,316
Buildings and Improvements	30,885
Net Improvements (Retirements Since Acquistion)	(1,004)
Carrying Amount at Which Carried
Land	4,397
Buildings and Improvements	29,799
Total	34,196	[2]
Accumulated Depreciation at December 31, 2011	4,022	[3]
Depreciable Life (Years)	51
457 Haddonfield Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	11,175	[1]
Initial Cost
Land	2,142
Buildings and Improvements	9,120
Net Improvements (Retirements Since Acquistion)	853
Carrying Amount at Which Carried
Land	2,142
Buildings and Improvements	9,973
Total	12,115	[2]
Accumulated Depreciation at December 31, 2011	4,138	[3]
Depreciable Life (Years)	40
220 Lake Drive East [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,144
Buildings and Improvements	8,798
Net Improvements (Retirements Since Acquistion)	863
Carrying Amount at Which Carried
Land	2,144
Buildings and Improvements	9,661
Total	11,805	[2]
Accumulated Depreciation at December 31, 2011	2,799	[3]
Depreciable Life (Years)	40
200 Lake Drive East [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,069
Buildings and Improvements	8,275
Net Improvements (Retirements Since Acquistion)	1,244
Carrying Amount at Which Carried
Land	2,068
Buildings and Improvements	9,520
Total	11,588	[2]
Accumulated Depreciation at December 31, 2011	2,559	[3]
Depreciable Life (Years)	40
210 Lake Drive East [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,645
Buildings and Improvements	6,579
Net Improvements (Retirements Since Acquistion)	1,332
Carrying Amount at Which Carried
Land	1,645
Buildings and Improvements	7,911
Total	9,556	[2]
Accumulated Depreciation at December 31, 2011	2,222	[3]
Depreciable Life (Years)	40
6 East Clementon Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,345
Buildings and Improvements	5,366
Net Improvements (Retirements Since Acquistion)	682
Carrying Amount at Which Carried
Land	1,345
Buildings and Improvements	6,048
Total	7,393	[2]
Accumulated Depreciation at December 31, 2011	2,303	[3]
Depreciable Life (Years)	40
20 East Clementon Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	769
Buildings and Improvements	3,055
Net Improvements (Retirements Since Acquistion)	582
Carrying Amount at Which Carried
Land	768
Buildings and Improvements	3,638
Total	4,406	[2]
Accumulated Depreciation at December 31, 2011	1,425	[3]
Depreciable Life (Years)	40
10 Foster Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	244
Buildings and Improvements	971
Net Improvements (Retirements Since Acquistion)	118
Carrying Amount at Which Carried
Land	244
Buildings and Improvements	1,089
Total	1,333	[2]
Accumulated Depreciation at December 31, 2011	450	[3]
Depreciable Life (Years)	40
7 Foster Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	231
Buildings and Improvements	921
Net Improvements (Retirements Since Acquistion)	16
Carrying Amount at Which Carried
Land	231
Buildings and Improvements	937
Total	1,168	[2]
Accumulated Depreciation at December 31, 2011	373	[3]
Depreciable Life (Years)	40
50 East Clementon Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	114
Buildings and Improvements	964
Net Improvements (Retirements Since Acquistion)	3
Carrying Amount at Which Carried
Land	114
Buildings and Improvements	967
Total	1,081	[2]
Accumulated Depreciation at December 31, 2011	383	[3]
Depreciable Life (Years)	40
2 Foster Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	185
Buildings and Improvements	730
Net Improvements (Retirements Since Acquistion)	16
Carrying Amount at Which Carried
Land	185
Buildings and Improvements	746
Total	931	[2]
Accumulated Depreciation at December 31, 2011	297	[3]
Depreciable Life (Years)	40
4 Foster Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	183
Buildings and Improvements	726
Net Improvements (Retirements Since Acquistion)	5
Carrying Amount at Which Carried
Land	182
Buildings and Improvements	732
Total	914	[2]
Accumulated Depreciation at December 31, 2011	290	[3]
Depreciable Life (Years)	40
1 Foster Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	93
Buildings and Improvements	364
Net Improvements (Retirements Since Acquistion)	76
Carrying Amount at Which Carried
Land	93
Buildings and Improvements	440
Total	533	[2]
Accumulated Depreciation at December 31, 2011	185	[3]
Depreciable Life (Years)	40
5 U.S. Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	21
Buildings and Improvements	81
Net Improvements (Retirements Since Acquistion)	3
Carrying Amount at Which Carried
Land	21
Buildings and Improvements	84
Total	105	[2]
Accumulated Depreciation at December 31, 2011	33	[3]
Depreciable Life (Years)	40
5 Foster Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	9
Buildings and Improvements	32
Net Improvements (Retirements Since Acquistion)	26
Carrying Amount at Which Carried
Land	9
Buildings and Improvements	58
Total	67	[2]
Accumulated Depreciation at December 31, 2011	23	[3]
Depreciable Life (Years)	40
1009 Lenox Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	4,876
Buildings and Improvements	19,284
Net Improvements (Retirements Since Acquistion)	4,373
Carrying Amount at Which Carried
Land	5,118
Buildings and Improvements	23,415
Total	28,533	[2]
Accumulated Depreciation at December 31, 2011	9,039	[3]
Depreciable Life (Years)	40
989 Lenox Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	3,701
Buildings and Improvements	14,802
Net Improvements (Retirements Since Acquistion)	1,420
Carrying Amount at Which Carried
Land	3,850
Buildings and Improvements	16,073
Total	19,923	[2]
Accumulated Depreciation at December 31, 2011	3,610	[3]
Depreciable Life (Years)	40
997 Lenox Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,410
Buildings and Improvements	9,700
Net Improvements (Retirements Since Acquistion)	4,442
Carrying Amount at Which Carried
Land	2,540
Buildings and Improvements	14,012
Total	16,552	[2]
Accumulated Depreciation at December 31, 2011	4,781	[3]
Depreciable Life (Years)	40
2000 Lenox Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,291
Buildings and Improvements	12,221
Net Improvements (Retirements Since Acquistion)	1,975
Carrying Amount at Which Carried
Land	2,684
Buildings and Improvements	13,803
Total	16,487	[2]
Accumulated Depreciation at December 31, 2011	3,499	[3]
Depreciable Life (Years)	40
993 Lenox Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,811
Buildings and Improvements	17,996
Net Improvements (Retirements Since Acquistion)	(4,369)
Carrying Amount at Which Carried
Land	2,960
Buildings and Improvements	13,478
Total	16,438	[2]
Accumulated Depreciation at December 31, 2011	5,196	[3]
Depreciable Life (Years)	40
1200 Lenox Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,071
Buildings and Improvements	12,967
Net Improvements (Retirements Since Acquistion)	1,238
Carrying Amount at Which Carried
Land	1,071
Buildings and Improvements	14,205
Total	15,276	[2]
Accumulated Depreciation at December 31, 2011	1,846	[3]
Depreciable Life (Years)	40
100 Lenox Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	0
Buildings and Improvements	0
Net Improvements (Retirements Since Acquistion)	12,103
Carrying Amount at Which Carried
Land	1,134
Buildings and Improvements	10,969
Total	12,103	[2]
Accumulated Depreciation at December 31, 2011	1,815	[3]
Depreciable Life (Years)	40
1000 Lenox Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,174
Buildings and Improvements	4,696
Net Improvements (Retirements Since Acquistion)	2,180
Carrying Amount at Which Carried
Land	1,244
Buildings and Improvements	6,806
Total	8,050	[2]
Accumulated Depreciation at December 31, 2011	2,677	[3]
Depreciable Life (Years)	40
1120 Executive Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,074
Buildings and Improvements	8,415
Net Improvements (Retirements Since Acquistion)	1,804
Carrying Amount at Which Carried
Land	2,074
Buildings and Improvements	10,219
Total	12,293	[2]
Accumulated Depreciation at December 31, 2011	4,200	[3]
Depreciable Life (Years)	40
Two Eves Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	818
Buildings and Improvements	3,461
Net Improvements (Retirements Since Acquistion)	178
Carrying Amount at Which Carried
Land	819
Buildings and Improvements	3,638
Total	4,457	[2]
Accumulated Depreciation at December 31, 2011	1,575	[3]
Depreciable Life (Years)	40
Five Eves Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	703
Buildings and Improvements	2,819
Net Improvements (Retirements Since Acquistion)	511
Carrying Amount at Which Carried
Land	703
Buildings and Improvements	3,330
Total	4,033	[2]
Accumulated Depreciation at December 31, 2011	1,392	[3]
Depreciable Life (Years)	40
Four B Eves Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	588
Buildings and Improvements	2,369
Net Improvements (Retirements Since Acquistion)	361
Carrying Amount at Which Carried
Land	589
Buildings and Improvements	2,729
Total	3,318	[2]
Accumulated Depreciation at December 31, 2011	1,180	[3]
Depreciable Life (Years)	40
Four A Eves Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	539
Buildings and Improvements	2,168
Net Improvements (Retirements Since Acquistion)	136
Carrying Amount at Which Carried
Land	538
Buildings and Improvements	2,305
Total	2,843	[2]
Accumulated Depreciation at December 31, 2011	1,011	[3]
Depreciable Life (Years)	40
308 Harper Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,643
Buildings and Improvements	6,663
Net Improvements (Retirements Since Acquistion)	1,070
Carrying Amount at Which Carried
Land	1,644
Buildings and Improvements	7,732
Total	9,376	[2]
Accumulated Depreciation at December 31, 2011	2,685	[3]
Depreciable Life (Years)	40
304 Harper Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	657
Buildings and Improvements	2,674
Net Improvements (Retirements Since Acquistion)	359
Carrying Amount at Which Carried
Land	657
Buildings and Improvements	3,033
Total	3,690	[2]
Accumulated Depreciation at December 31, 2011	1,161	[3]
Depreciable Life (Years)	40
700 East Gate Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	3,569
Buildings and Improvements	14,436
Net Improvements (Retirements Since Acquistion)	2,122
Carrying Amount at Which Carried
Land	3,568
Buildings and Improvements	16,559
Total	20,127	[2]
Accumulated Depreciation at December 31, 2011	6,205	[3]
Depreciable Life (Years)	40
10000 Midlantic Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	3,206
Buildings and Improvements	12,857
Net Improvements (Retirements Since Acquistion)	1,473
Carrying Amount at Which Carried
Land	3,206
Buildings and Improvements	14,330
Total	17,536	[2]
Accumulated Depreciation at December 31, 2011	6,306	[3]
Depreciable Life (Years)	40
15000 Midlantic Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	3,061
Buildings and Improvements	12,254
Net Improvements (Retirements Since Acquistion)	1,070
Carrying Amount at Which Carried
Land	3,061
Buildings and Improvements	13,324
Total	16,385	[2]
Accumulated Depreciation at December 31, 2011	5,351	[3]
Depreciable Life (Years)	40
1000 Atrium Way [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,061
Buildings and Improvements	8,180
Net Improvements (Retirements Since Acquistion)	3,583
Carrying Amount at Which Carried
Land	2,062
Buildings and Improvements	11,762
Total	13,824	[2]
Accumulated Depreciation at December 31, 2011	4,788	[3]
Depreciable Life (Years)	40
1000 Howard Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,297
Buildings and Improvements	9,288
Net Improvements (Retirements Since Acquistion)	1,378
Carrying Amount at Which Carried
Land	2,297
Buildings and Improvements	10,666
Total	12,963	[2]
Accumulated Depreciation at December 31, 2011	4,294	[3]
Depreciable Life (Years)	40
2000 Midlantic Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,202
Buildings and Improvements	8,823
Net Improvements (Retirements Since Acquistion)	1,905
Carrying Amount at Which Carried
Land	2,203
Buildings and Improvements	10,727
Total	12,930	[2]
Accumulated Depreciation at December 31, 2011	3,953	[3]
Depreciable Life (Years)	40
701 East Gate Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,736
Buildings and Improvements	6,877
Net Improvements (Retirements Since Acquistion)	1,277
Carrying Amount at Which Carried
Land	1,736
Buildings and Improvements	8,154
Total	9,890	[2]
Accumulated Depreciation at December 31, 2011	2,843	[3]
Depreciable Life (Years)	40
307 Fellowship Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,565
Buildings and Improvements	6,342
Net Improvements (Retirements Since Acquistion)	1,295
Carrying Amount at Which Carried
Land	1,564
Buildings and Improvements	7,638
Total	9,202	[2]
Accumulated Depreciation at December 31, 2011	2,658	[3]
Depreciable Life (Years)	40
9000 Midlantic Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,472
Buildings and Improvements	5,895
Net Improvements (Retirements Since Acquistion)	1,785
Carrying Amount at Which Carried
Land	1,471
Buildings and Improvements	7,681
Total	9,152	[2]
Accumulated Depreciation at December 31, 2011	2,608	[3]
Depreciable Life (Years)	40
305 Fellowship Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,421
Buildings and Improvements	5,768
Net Improvements (Retirements Since Acquistion)	1,440
Carrying Amount at Which Carried
Land	1,421
Buildings and Improvements	7,208
Total	8,629	[2]
Accumulated Depreciation at December 31, 2011	3,050	[3]
Depreciable Life (Years)	40
309 Fellowship Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,518
Buildings and Improvements	6,154
Net Improvements (Retirements Since Acquistion)	564
Carrying Amount at Which Carried
Land	1,518
Buildings and Improvements	6,718
Total	8,236	[2]
Accumulated Depreciation at December 31, 2011	2,472	[3]
Depreciable Life (Years)	40
303 Fellowship Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,493
Buildings and Improvements	6,055
Net Improvements (Retirements Since Acquistion)	567
Carrying Amount at Which Carried
Land	1,493
Buildings and Improvements	6,622
Total	8,115	[2]
Accumulated Depreciation at December 31, 2011	2,441	[3]
Depreciable Life (Years)	40
1000 Bishops Gate [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	934
Buildings and Improvements	6,287
Net Improvements (Retirements Since Acquistion)	427
Carrying Amount at Which Carried
Land	934
Buildings and Improvements	6,714
Total	7,648	[2]
Accumulated Depreciation at December 31, 2011	1,755	[3]
Depreciable Life (Years)	40
161 Gaither Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,016
Buildings and Improvements	4,064
Net Improvements (Retirements Since Acquistion)	818
Carrying Amount at Which Carried
Land	1,016
Buildings and Improvements	4,882
Total	5,898	[2]
Accumulated Depreciation at December 31, 2011	1,578	[3]
Depreciable Life (Years)	40
4000 Midlantic Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	714
Buildings and Improvements	5,085
Net Improvements (Retirements Since Acquistion)	(1,403)
Carrying Amount at Which Carried
Land	714
Buildings and Improvements	3,682
Total	4,396	[2]
Accumulated Depreciation at December 31, 2011	1,810	[3]
Depreciable Life (Years)	40
815 East Gate Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	636
Buildings and Improvements	2,584
Net Improvements (Retirements Since Acquistion)	253
Carrying Amount at Which Carried
Land	636
Buildings and Improvements	2,837
Total	3,473	[2]
Accumulated Depreciation at December 31, 2011	1,092	[3]
Depreciable Life (Years)	40
817 East Gate Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	611
Buildings and Improvements	2,426
Net Improvements (Retirements Since Acquistion)	360
Carrying Amount at Which Carried
Land	612
Buildings and Improvements	2,785
Total	3,397	[2]
Accumulated Depreciation at December 31, 2011	1,096	[3]
Depreciable Life (Years)	40
400 Commerce Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,528
Buildings and Improvements	9,220
Net Improvements (Retirements Since Acquistion)	1,180
Carrying Amount at Which Carried
Land	2,528
Buildings and Improvements	10,400
Total	12,928	[2]
Accumulated Depreciation at December 31, 2011	3,000	[3]
Depreciable Life (Years)	40
200 Commerce Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	911
Buildings and Improvements	4,414
Net Improvements (Retirements Since Acquistion)	1,018
Carrying Amount at Which Carried
Land	911
Buildings and Improvements	5,432
Total	6,343	[2]
Accumulated Depreciation at December 31, 2011	1,676	[3]
Depreciable Life (Years)	40
100 Commerce Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,160
Buildings and Improvements	4,633
Net Improvements (Retirements Since Acquistion)	454
Carrying Amount at Which Carried
Land	1,159
Buildings and Improvements	5,088
Total	6,247	[2]
Accumulated Depreciation at December 31, 2011	2,116	[3]
Depreciable Life (Years)	40
Main Street-Plaza 1000 [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,732
Buildings and Improvements	10,942
Net Improvements (Retirements Since Acquistion)	3,446
Carrying Amount at Which Carried
Land	2,732
Buildings and Improvements	14,388
Total	17,120	[2]
Accumulated Depreciation at December 31, 2011	6,143	[3]
Depreciable Life (Years)	40
Main Street-Piazza [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	696
Buildings and Improvements	2,802
Net Improvements (Retirements Since Acquistion)	60
Carrying Amount at Which Carried
Land	696
Buildings and Improvements	2,862
Total	3,558	[2]
Accumulated Depreciation at December 31, 2011	1,233	[3]
Depreciable Life (Years)	40
Main Street-Promenade [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	531
Buildings and Improvements	2,052
Net Improvements (Retirements Since Acquistion)	363
Carrying Amount at Which Carried
Land	531
Buildings and Improvements	2,415
Total	2,946	[2]
Accumulated Depreciation at December 31, 2011	916	[3]
Depreciable Life (Years)	40
920 North King Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	6,141
Buildings and Improvements	21,140
Net Improvements (Retirements Since Acquistion)	1,232
Carrying Amount at Which Carried
Land	6,142
Buildings and Improvements	22,371
Total	28,513	[2]
Accumulated Depreciation at December 31, 2011	6,432	[3]
Depreciable Life (Years)	30
300 Delaware Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	6,368
Buildings and Improvements	13,739
Net Improvements (Retirements Since Acquistion)	2,942
Carrying Amount at Which Carried
Land	6,369
Buildings and Improvements	16,680
Total	23,049	[2]
Accumulated Depreciation at December 31, 2011	5,121	[3]
Depreciable Life (Years)	23
Two Righter Parkway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,802
Buildings and Improvements	11,217
Net Improvements (Retirements Since Acquistion)	5,255
Carrying Amount at Which Carried
Land	2,803
Buildings and Improvements	16,471
Total	19,274	[2]
Accumulated Depreciation at December 31, 2011	2,361	[3]
Depreciable Life (Years)	40
One Righter Parkway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,545
Buildings and Improvements	10,195
Net Improvements (Retirements Since Acquistion)	4,773
Carrying Amount at Which Carried
Land	2,546
Buildings and Improvements	14,967
Total	17,513	[2]
Accumulated Depreciation at December 31, 2011	7,070	[3]
Depreciable Life (Years)	40
4364 South Alston Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,622
Buildings and Improvements	6,419
Net Improvements (Retirements Since Acquistion)	892
Carrying Amount at Which Carried
Land	1,580
Buildings and Improvements	7,353
Total	8,933	[2]
Accumulated Depreciation at December 31, 2011	2,625	[3]
Depreciable Life (Years)	40
4805 Lake Brooke Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,640
Buildings and Improvements	6,567
Net Improvements (Retirements Since Acquistion)	1,373
Carrying Amount at Which Carried
Land	1,640
Buildings and Improvements	7,940
Total	9,580	[2]
Accumulated Depreciation at December 31, 2011	3,220	[3]
Depreciable Life (Years)	40
Overlook II [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	791
Buildings and Improvements	4,503
Net Improvements (Retirements Since Acquistion)	62
Carrying Amount at Which Carried
Land	790
Buildings and Improvements	4,565
Total	5,355	[2]
Accumulated Depreciation at December 31, 2011	188	[3]
Depreciable Life (Years)	40
Overlook I [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	791
Buildings and Improvements	3,976
Net Improvements (Retirements Since Acquistion)	93
Carrying Amount at Which Carried
Land	790
Buildings and Improvements	4,069
Total	4,859	[2]
Accumulated Depreciation at December 31, 2011	181	[3]
Depreciable Life (Years)	40
2812 Emerywood Parkway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,069
Buildings and Improvements	4,281
Net Improvements (Retirements Since Acquistion)	1,043
Carrying Amount at Which Carried
Land	1,069
Buildings and Improvements	5,324
Total	6,393	[2]
Accumulated Depreciation at December 31, 2011	2,226	[3]
Depreciable Life (Years)	40
300 Arboretum Place [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	5,450
Buildings and Improvements	21,892
Net Improvements (Retirements Since Acquistion)	3,528
Carrying Amount at Which Carried
Land	5,450
Buildings and Improvements	25,420
Total	30,870	[2]
Accumulated Depreciation at December 31, 2011	9,639	[3]
Depreciable Life (Years)	40
7501 Boulders View Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	4,669
Buildings and Improvements	19,699
Net Improvements (Retirements Since Acquistion)	1,952
Carrying Amount at Which Carried
Land	4,925
Buildings and Improvements	21,395
Total	26,320	[2]
Accumulated Depreciation at December 31, 2011	2,510	[3]
Depreciable Life (Years)	40
7300 Beaufont Springs Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	4,672
Buildings and Improvements	19,689
Net Improvements (Retirements Since Acquistion)	670
Carrying Amount at Which Carried
Land	4,922
Buildings and Improvements	20,109
Total	25,031	[2]
Accumulated Depreciation at December 31, 2011	2,256	[3]
Depreciable Life (Years)	40
6800 Paragon Place [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	4,552
Buildings and Improvements	18,414
Net Improvements (Retirements Since Acquistion)	1,549
Carrying Amount at Which Carried
Land	4,552
Buildings and Improvements	19,963
Total	24,515	[2]
Accumulated Depreciation at December 31, 2011	3,110	[3]
Depreciable Life (Years)	40
6802 Paragon Place [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,917
Buildings and Improvements	11,454
Net Improvements (Retirements Since Acquistion)	2,469
Carrying Amount at Which Carried
Land	2,917
Buildings and Improvements	13,923
Total	16,840	[2]
Accumulated Depreciation at December 31, 2011	3,638	[3]
Depreciable Life (Years)	40
1025 Boulders Parkway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,574
Buildings and Improvements	11,297
Net Improvements (Retirements Since Acquistion)	1,146
Carrying Amount at Which Carried
Land	2,825
Buildings and Improvements	12,192
Total	15,017	[2]
Accumulated Depreciation at December 31, 2011	1,364	[3]
Depreciable Life (Years)	40
2100-2116 West Laburnam Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,482
Buildings and Improvements	8,846
Net Improvements (Retirements Since Acquistion)	3,073
Carrying Amount at Which Carried
Land	2,482
Buildings and Improvements	11,919
Total	14,401	[2]
Accumulated Depreciation at December 31, 2011	4,497	[3]
Depreciable Life (Years)	40
7401 Beaufont Springs Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,349
Buildings and Improvements	10,396
Net Improvements (Retirements Since Acquistion)	717
Carrying Amount at Which Carried
Land	2,599
Buildings and Improvements	10,863
Total	13,462	[2]
Accumulated Depreciation at December 31, 2011	1,201	[3]
Depreciable Life (Years)	40
7325 Beaufont Springs Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,344
Buildings and Improvements	10,377
Net Improvements (Retirements Since Acquistion)	502
Carrying Amount at Which Carried
Land	2,594
Buildings and Improvements	10,629
Total	13,223	[2]
Accumulated Depreciation at December 31, 2011	1,307	[3]
Depreciable Life (Years)	40
6806 Paragon Place [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	0
Buildings and Improvements	10,288
Net Improvements (Retirements Since Acquistion)	827
Carrying Amount at Which Carried
Land	403
Buildings and Improvements	10,712
Total	11,115	[2]
Accumulated Depreciation at December 31, 2011	2,573	[3]
Depreciable Life (Years)	40
9011 Arboretum Parkway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,857
Buildings and Improvements	7,702
Net Improvements (Retirements Since Acquistion)	832
Carrying Amount at Which Carried
Land	1,856
Buildings and Improvements	8,535
Total	10,391	[2]
Accumulated Depreciation at December 31, 2011	3,333	[3]
Depreciable Life (Years)	40
2511 Brittons Hill Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,202
Buildings and Improvements	4,820
Net Improvements (Retirements Since Acquistion)	1,472
Carrying Amount at Which Carried
Land	1,202
Buildings and Improvements	6,292
Total	7,494	[2]
Accumulated Depreciation at December 31, 2011	2,472	[3]
Depreciable Life (Years)	40
9100 Arboretum Parkway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,362
Buildings and Improvements	5,489
Net Improvements (Retirements Since Acquistion)	565
Carrying Amount at Which Carried
Land	1,362
Buildings and Improvements	6,054
Total	7,416	[2]
Accumulated Depreciation at December 31, 2011	2,298	[3]
Depreciable Life (Years)	40
100 Gateway Centre Parkway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	391
Buildings and Improvements	5,410
Net Improvements (Retirements Since Acquistion)	885
Carrying Amount at Which Carried
Land	391
Buildings and Improvements	6,295
Total	6,686	[2]
Accumulated Depreciation at December 31, 2011	1,878	[3]
Depreciable Life (Years)	40
9200 Arboretum Parkway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	985
Buildings and Improvements	3,973
Net Improvements (Retirements Since Acquistion)	1,353
Carrying Amount at Which Carried
Land	984
Buildings and Improvements	5,327
Total	6,311	[2]
Accumulated Depreciation at December 31, 2011	1,819	[3]
Depreciable Life (Years)	40
9210 Arboretum Parkway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,110
Buildings and Improvements	4,474
Net Improvements (Retirements Since Acquistion)	486
Carrying Amount at Which Carried
Land	1,110
Buildings and Improvements	4,960
Total	6,070	[2]
Accumulated Depreciation at December 31, 2011	1,839	[3]
Depreciable Life (Years)	40
2201-2245 Tomlynn Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,020
Buildings and Improvements	4,067
Net Improvements (Retirements Since Acquistion)	447
Carrying Amount at Which Carried
Land	1,019
Buildings and Improvements	4,515
Total	5,534	[2]
Accumulated Depreciation at December 31, 2011	1,620	[3]
Depreciable Life (Years)	40
9211 Arboretum Parkway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	582
Buildings and Improvements	2,433
Net Improvements (Retirements Since Acquistion)	252
Carrying Amount at Which Carried
Land	582
Buildings and Improvements	2,685
Total	3,267	[2]
Accumulated Depreciation at December 31, 2011	1,048	[3]
Depreciable Life (Years)	40
2212-2224 Tomlynn Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	502
Buildings and Improvements	2,014
Net Improvements (Retirements Since Acquistion)	353
Carrying Amount at Which Carried
Land	502
Buildings and Improvements	2,367
Total	2,869	[2]
Accumulated Depreciation at December 31, 2011	779	[3]
Depreciable Life (Years)	40
2244 Dabney Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	550
Buildings and Improvements	2,203
Net Improvements (Retirements Since Acquistion)	37
Carrying Amount at Which Carried
Land	550
Buildings and Improvements	2,240
Total	2,790	[2]
Accumulated Depreciation at December 31, 2011	837	[3]
Depreciable Life (Years)	40
2248 Dabney Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	512
Buildings and Improvements	2,049
Net Improvements (Retirements Since Acquistion)	223
Carrying Amount at Which Carried
Land	512
Buildings and Improvements	2,272
Total	2,784	[2]
Accumulated Depreciation at December 31, 2011	854	[3]
Depreciable Life (Years)	40
2221-2245 Dabney Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	530
Buildings and Improvements	2,123
Net Improvements (Retirements Since Acquistion)	80
Carrying Amount at Which Carried
Land	529
Buildings and Improvements	2,204
Total	2,733	[2]
Accumulated Depreciation at December 31, 2011	804	[3]
Depreciable Life (Years)	40
2277 Dabney Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	507
Buildings and Improvements	2,034
Net Improvements (Retirements Since Acquistion)	61
Carrying Amount at Which Carried
Land	507
Buildings and Improvements	2,095
Total	2,602	[2]
Accumulated Depreciation at December 31, 2011	751	[3]
Depreciable Life (Years)	40
2246 Dabney Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	455
Buildings and Improvements	1,822
Net Improvements (Retirements Since Acquistion)	18
Carrying Amount at Which Carried
Land	455
Buildings and Improvements	1,840
Total	2,295	[2]
Accumulated Depreciation at December 31, 2011	682	[3]
Depreciable Life (Years)	40
2161-2179 Tomlynn Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	423
Buildings and Improvements	1,695
Net Improvements (Retirements Since Acquistion)	68
Carrying Amount at Which Carried
Land	423
Buildings and Improvements	1,763
Total	2,186	[2]
Accumulated Depreciation at December 31, 2011	640	[3]
Depreciable Life (Years)	40
2251 Dabney Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	387
Buildings and Improvements	1,552
Net Improvements (Retirements Since Acquistion)	138
Carrying Amount at Which Carried
Land	387
Buildings and Improvements	1,690
Total	2,077	[2]
Accumulated Depreciation at December 31, 2011	636	[3]
Depreciable Life (Years)	40
2256 Dabney Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	356
Buildings and Improvements	1,427
Net Improvements (Retirements Since Acquistion)	273
Carrying Amount at Which Carried
Land	356
Buildings and Improvements	1,700
Total	2,056	[2]
Accumulated Depreciation at December 31, 2011	676	[3]
Depreciable Life (Years)	40
2130-2146 Tomlynn Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	353
Buildings and Improvements	1,416
Net Improvements (Retirements Since Acquistion)	213
Carrying Amount at Which Carried
Land	353
Buildings and Improvements	1,629
Total	1,982	[2]
Accumulated Depreciation at December 31, 2011	681	[3]
Depreciable Life (Years)	40
2120 Tomlynn Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	281
Buildings and Improvements	1,125
Net Improvements (Retirements Since Acquistion)	204
Carrying Amount at Which Carried
Land	280
Buildings and Improvements	1,330
Total	1,610	[2]
Accumulated Depreciation at December 31, 2011	475	[3]
Depreciable Life (Years)	40
2240 Dabney Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	264
Buildings and Improvements	1,059
Net Improvements (Retirements Since Acquistion)	11
Carrying Amount at Which Carried
Land	264
Buildings and Improvements	1,069
Total	1,333	[2]
Accumulated Depreciation at December 31, 2011	396	[3]
Depreciable Life (Years)	40
Boulders Land [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,256
Buildings and Improvements	0
Net Improvements (Retirements Since Acquistion)	3
Carrying Amount at Which Carried
Land	1,259
Buildings and Improvements	0
Total	1,259	[2]
Accumulated Depreciation at December 31, 2011	0	[3]
5780 & 5790 Fleet Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	7,073
Buildings and Improvements	22,907
Net Improvements (Retirements Since Acquistion)	3,435
Carrying Amount at Which Carried
Land	7,516
Buildings and Improvements	25,899
Total	33,415	[2]
Accumulated Depreciation at December 31, 2011	3,596	[3]
Depreciable Life (Years)	55
5900 & 5950 La Place Court [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	3,706
Buildings and Improvements	11,185
Net Improvements (Retirements Since Acquistion)	2,090
Carrying Amount at Which Carried
Land	3,955
Buildings and Improvements	13,026
Total	16,981	[2]
Accumulated Depreciation at December 31, 2011	2,090	[3]
Depreciable Life (Years)	48
5963 La Place Court [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,824
Buildings and Improvements	9,413
Net Improvements (Retirements Since Acquistion)	1,662
Carrying Amount at Which Carried
Land	2,999
Buildings and Improvements	10,900
Total	13,899	[2]
Accumulated Depreciation at December 31, 2011	1,647	[3]
Depreciable Life (Years)	55
5973 Avenida Encinas [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,121
Buildings and Improvements	8,361
Net Improvements (Retirements Since Acquistion)	1,383
Carrying Amount at Which Carried
Land	2,256
Buildings and Improvements	9,609
Total	11,865	[2]
Accumulated Depreciation at December 31, 2011	1,803	[3]
Depreciable Life (Years)	45
2035 Corte Del Nogal [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	3,261
Buildings and Improvements	6,077
Net Improvements (Retirements Since Acquistion)	1,250
Carrying Amount at Which Carried
Land	3,499
Buildings and Improvements	7,089
Total	10,588	[2]
Accumulated Depreciation at December 31, 2011	1,484	[3]
Depreciable Life (Years)	39
1200 Concord Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	6,395
Buildings and Improvements	24,664
Net Improvements (Retirements Since Acquistion)	235
Carrying Amount at Which Carried
Land	6,515
Buildings and Improvements	24,778
Total	31,293	[2]
Accumulated Depreciation at December 31, 2011	4,215	[3]
Depreciable Life (Years)	34
1220 Concord Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	6,476
Buildings and Improvements	24,966
Net Improvements (Retirements Since Acquistion)	(332)
Carrying Amount at Which Carried
Land	6,476
Buildings and Improvements	24,634
Total	31,110	[2]
Accumulated Depreciation at December 31, 2011	3,911	[3]
Depreciable Life (Years)	34
155 Grand Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	13,556
Buildings and Improvements	54,266
Net Improvements (Retirements Since Acquistion)	4,482
Carrying Amount at Which Carried
Land	13,555
Buildings and Improvements	58,749
Total	72,304	[2]
Accumulated Depreciation at December 31, 2011	7,863	[3]
Depreciable Life (Years)	40
Two Kaiser Plaza [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	7,841
Buildings and Improvements	0
Net Improvements (Retirements Since Acquistion)	0
Carrying Amount at Which Carried
Land	7,841
Buildings and Improvements	0
Total	7,841	[2]
Accumulated Depreciation at December 31, 2011	0	[3]
Oakland Lot B [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	4,342
Buildings and Improvements	0
Net Improvements (Retirements Since Acquistion)	0
Carrying Amount at Which Carried
Land	4,342
Buildings and Improvements	0
Total	4,342	[2]
Accumulated Depreciation at December 31, 2011	0	[3]
16870 W Bernardo Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	2,979
Buildings and Improvements	15,896
Net Improvements (Retirements Since Acquistion)	1,766
Carrying Amount at Which Carried
Land	3,154
Buildings and Improvements	17,487
Total	20,641	[2]
Accumulated Depreciation at December 31, 2011	2,562	[3]
Depreciable Life (Years)	56
1250 Capital of Texas Hwy South [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	5,152
Buildings and Improvements	37,928
Net Improvements (Retirements Since Acquistion)	5,826
Carrying Amount at Which Carried
Land	5,247
Buildings and Improvements	43,659
Total	48,906	[2]
Accumulated Depreciation at December 31, 2011	7,063	[3]
Depreciable Life (Years)	52
1301 Mopac Expressway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	4,188
Buildings and Improvements	41,229
Net Improvements (Retirements Since Acquistion)	(595)
Carrying Amount at Which Carried
Land	4,251
Buildings and Improvements	40,571
Total	44,822	[2]
Accumulated Depreciation at December 31, 2011	5,732	[3]
Depreciable Life (Years)	55
1221 Mopac Expressway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	3,290
Buildings and Improvements	31,548
Net Improvements (Retirements Since Acquistion)	4,228
Carrying Amount at Which Carried
Land	3,369
Buildings and Improvements	35,696
Total	39,065	[2]
Accumulated Depreciation at December 31, 2011	3,900	[3]
Depreciable Life (Years)	55
1601 Mopac Expressway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	3,538
Buildings and Improvements	34,346
Net Improvements (Retirements Since Acquistion)	220
Carrying Amount at Which Carried
Land	3,605
Buildings and Improvements	34,499
Total	38,104	[2]
Accumulated Depreciation at December 31, 2011	4,390	[3]
Depreciable Life (Years)	54
1501 South Mopac Expressway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	3,698
Buildings and Improvements	34,912
Net Improvements (Retirements Since Acquistion)	(2,202)
Carrying Amount at Which Carried
Land	3,767
Buildings and Improvements	32,640
Total	36,407	[2]
Accumulated Depreciation at December 31, 2011	3,889	[3]
Depreciable Life (Years)	53
3711 South Mopac Expressway - II [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,688
Buildings and Improvements	19,229
Net Improvements (Retirements Since Acquistion)	4,316
Carrying Amount at Which Carried
Land	1,688
Buildings and Improvements	23,545
Total	25,233	[2]
Accumulated Depreciation at December 31, 2011	3,660	[3]
Depreciable Life (Years)	40
3711 South Mopac Expressway - I [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2011	0	[1]
Initial Cost
Land	1,688
Buildings and Improvements	21,011
Net Improvements (Retirements Since Acquistion)	2,451
Carrying Amount at Which Carried
Land	1,688
Buildings and Improvements	23,462
Total	25,150	[2]
Accumulated Depreciation at December 31, 2011	$ 2,262	[3]
Depreciable Life (Years)	40

[1] Excludes the effect of any net interest premium/(discount).

[2] Reconciliation of Real Estate:The following table reconciles the real estate investments from January 1, 2009 to December 31, 2011 (in thousands): 2011 2010 2009Balance at beginning of year$4,834,111 $4,512,618 $4,608,320Additions: Acquisitions31,454 102,475 —Capital expenditures133,550 336,281 80,506Less: Dispositions(206,035) (117,263) (176,208)Balance at end of year$4,793,080 $4,834,111 $4,512,618

[3] Reconciliation of Accumulated Depreciation:The following table reconciles the accumulated depreciation on real estate investments from January 1, 2009 to December 31, 2011 (in thousands): 2011 2010 2009Balance at beginning of year$776,078 $716,957 $639,688Additions: Depreciation expense — continuing operations157,691 133,740 141,309Depreciation expense — discontinued operations1,185 1,554 6,494Less: Dispositions(69,244) (76,173) (70,534)Balance at end of year$865,710 $776,078 $716,957

[4] This property was contributed to an unconsolidated real estate venture, however, the Company will continue to consolidate this property due to its continuing involvement in this property resulting from its ongoing lease at this property and its 50% ownership interest in the venture. Please see Note 3 to the consolidated financial financial statements for additional information.