Schedule III - Real Estate and Accumulated Depreciation (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	$ 443,942
Initial Cost [Abstract]
Land	651,264
Buildings and Improvements	3,533,200
Net Improvements (Retirements) Since Acquisition	541,708
Carrying Amount at Which Carried [Abstract]
Land	662,107
Buildings and Improvements	4,064,062
Total	4,726,169
Accumulated Depreciation at December 31, 2012	954,665
400 Berwyn Park [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,657
Buildings and Improvements	4,462
Net Improvements (Retirements) Since Acquisition	13,975
Carrying Amount at Which Carried [Abstract]
Land	2,657
Buildings and Improvements	18,438
Total	21,094
Accumulated Depreciation at December 31, 2012	5,183
Depreciable Life (Years)	40 years
300 Berwyn Park [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,206
Buildings and Improvements	13,422
Net Improvements (Retirements) Since Acquisition	4,080
Carrying Amount at Which Carried [Abstract]
Land	2,206
Buildings and Improvements	17,502
Total	19,708
Accumulated Depreciation at December 31, 2012	7,213
Depreciable Life (Years)	40 years
1050 Westlakes Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,611
Buildings and Improvements	10,445
Net Improvements (Retirements) Since Acquisition	5,046
Carrying Amount at Which Carried [Abstract]
Land	2,611
Buildings and Improvements	15,491
Total	18,102
Accumulated Depreciation at December 31, 2012	6,542
Depreciable Life (Years)	40 years
1200 Swedesford Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,595
Buildings and Improvements	11,809
Net Improvements (Retirements) Since Acquisition	3,472
Carrying Amount at Which Carried [Abstract]
Land	2,595
Buildings and Improvements	15,281
Total	17,876
Accumulated Depreciation at December 31, 2012	4,483
Depreciable Life (Years)	40 years
200 Berwyn Park [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,533
Buildings and Improvements	9,460
Net Improvements (Retirements) Since Acquisition	1,734
Carrying Amount at Which Carried [Abstract]
Land	1,533
Buildings and Improvements	11,193
Total	12,727
Accumulated Depreciation at December 31, 2012	4,829
Depreciable Life (Years)	40 years
1180 Swedesford Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,086
Buildings and Improvements	8,342
Net Improvements (Retirements) Since Acquisition	1,653
Carrying Amount at Which Carried [Abstract]
Land	2,086
Buildings and Improvements	9,995
Total	12,081
Accumulated Depreciation at December 31, 2012	2,896
Depreciable Life (Years)	40 years
100 Berwyn Park [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,180
Buildings and Improvements	7,290
Net Improvements (Retirements) Since Acquisition	2,019
Carrying Amount at Which Carried [Abstract]
Land	1,180
Buildings and Improvements	9,309
Total	10,489
Accumulated Depreciation at December 31, 2012	3,977
Depreciable Life (Years)	40 years
1160 Swedesford Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,781
Buildings and Improvements	7,124
Net Improvements (Retirements) Since Acquisition	1,006
Carrying Amount at Which Carried [Abstract]
Land	1,781
Buildings and Improvements	8,130
Total	9,911
Accumulated Depreciation at December 31, 2012	2,922
Depreciable Life (Years)	40 years
1100 Cassett Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,695
Buildings and Improvements	6,779
Net Improvements (Retirements) Since Acquisition	102
Carrying Amount at Which Carried [Abstract]
Land	1,695
Buildings and Improvements	6,882
Total	8,576
Accumulated Depreciation at December 31, 2012	1,999
Depreciable Life (Years)	40 years
980 Harvest Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	3,304
Buildings and Improvements	16,960
Net Improvements (Retirements) Since Acquisition	(541)
Carrying Amount at Which Carried [Abstract]
Land	3,304
Buildings and Improvements	16,420
Total	19,723
Accumulated Depreciation at December 31, 2012	5,838
Depreciable Life (Years)	40 years
925 Harvest Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,671
Buildings and Improvements	6,606
Net Improvements (Retirements) Since Acquisition	771
Carrying Amount at Which Carried [Abstract]
Land	1,671
Buildings and Improvements	7,377
Total	9,048
Accumulated Depreciation at December 31, 2012	3,071
Depreciable Life (Years)	40 years
920 Harvest Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,209
Buildings and Improvements	6,595
Net Improvements (Retirements) Since Acquisition	(310)
Carrying Amount at Which Carried [Abstract]
Land	1,208
Buildings and Improvements	6,286
Total	7,494
Accumulated Depreciation at December 31, 2012	2,876
Depreciable Life (Years)	40 years
426 Lancaster Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,689
Buildings and Improvements	6,756
Net Improvements (Retirements) Since Acquisition	396
Carrying Amount at Which Carried [Abstract]
Land	1,689
Buildings and Improvements	7,152
Total	8,841
Accumulated Depreciation at December 31, 2012	3,067
Depreciable Life (Years)	40 years
52 Swedesford Square [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	4,241
Buildings and Improvements	16,579
Net Improvements (Retirements) Since Acquisition	1,676
Carrying Amount at Which Carried [Abstract]
Land	4,241
Buildings and Improvements	18,255
Total	22,496
Accumulated Depreciation at December 31, 2012	6,912
Depreciable Life (Years)	40 years
100 Arrandale Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	970
Buildings and Improvements	3,878
Net Improvements (Retirements) Since Acquisition	0
Carrying Amount at Which Carried [Abstract]
Land	970
Buildings and Improvements	3,878
Total	4,848
Accumulated Depreciation at December 31, 2012	1,139
Depreciable Life (Years)	40 years
One Progress Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,399
Buildings and Improvements	5,629
Net Improvements (Retirements) Since Acquisition	5,107
Carrying Amount at Which Carried [Abstract]
Land	1,399
Buildings and Improvements	10,736
Total	12,135
Accumulated Depreciation at December 31, 2012	3,301
Depreciable Life (Years)	40 years
500 Enterprise Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,303
Buildings and Improvements	5,188
Net Improvements (Retirements) Since Acquisition	3,229
Carrying Amount at Which Carried [Abstract]
Land	1,303
Buildings and Improvements	8,416
Total	9,720
Accumulated Depreciation at December 31, 2012	3,071
Depreciable Life (Years)	40 years
640 Freedom Business Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	4,222
Buildings and Improvements	16,891
Net Improvements (Retirements) Since Acquisition	3,338
Carrying Amount at Which Carried [Abstract]
Land	4,222
Buildings and Improvements	20,229
Total	24,451
Accumulated Depreciation at December 31, 2012	8,279
Depreciable Life (Years)	40 years
555 Croton Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	4,486
Buildings and Improvements	17,943
Net Improvements (Retirements) Since Acquisition	1,325
Carrying Amount at Which Carried [Abstract]
Land	4,486
Buildings and Improvements	19,268
Total	23,754
Accumulated Depreciation at December 31, 2012	5,807
Depreciable Life (Years)	40 years
630 Allendale Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,836
Buildings and Improvements	4,028
Net Improvements (Retirements) Since Acquisition	12,025
Carrying Amount at Which Carried [Abstract]
Land	2,636
Buildings and Improvements	16,253
Total	18,889
Accumulated Depreciation at December 31, 2012	4,769
Depreciable Life (Years)	40 years
620 Freedom Business Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,770
Buildings and Improvements	11,014
Net Improvements (Retirements) Since Acquisition	3,415
Carrying Amount at Which Carried [Abstract]
Land	2,770
Buildings and Improvements	14,430
Total	17,199
Accumulated Depreciation at December 31, 2012	6,750
Depreciable Life (Years)	40 years
1000 First Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,772
Buildings and Improvements	10,936
Net Improvements (Retirements) Since Acquisition	3,230
Carrying Amount at Which Carried [Abstract]
Land	2,772
Buildings and Improvements	14,166
Total	16,938
Accumulated Depreciation at December 31, 2012	6,046
Depreciable Life (Years)	40 years
1060 First Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,712
Buildings and Improvements	10,953
Net Improvements (Retirements) Since Acquisition	2,459
Carrying Amount at Which Carried [Abstract]
Land	2,712
Buildings and Improvements	13,412
Total	16,124
Accumulated Depreciation at December 31, 2012	5,510
Depreciable Life (Years)	40 years
630 Freedom Business Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,773
Buildings and Improvements	11,144
Net Improvements (Retirements) Since Acquisition	1,787
Carrying Amount at Which Carried [Abstract]
Land	2,773
Buildings and Improvements	12,931
Total	15,704
Accumulated Depreciation at December 31, 2012	5,365
Depreciable Life (Years)	40 years
1040 First Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,860
Buildings and Improvements	11,282
Net Improvements (Retirements) Since Acquisition	839
Carrying Amount at Which Carried [Abstract]
Land	2,860
Buildings and Improvements	12,121
Total	14,981
Accumulated Depreciation at December 31, 2012	4,608
Depreciable Life (Years)	40 years
1020 First Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,168
Buildings and Improvements	8,576
Net Improvements (Retirements) Since Acquisition	3,885
Carrying Amount at Which Carried [Abstract]
Land	2,168
Buildings and Improvements	12,461
Total	14,629
Accumulated Depreciation at December 31, 2012	5,426
Depreciable Life (Years)	40 years
610 Freedom Business Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,017
Buildings and Improvements	8,070
Net Improvements (Retirements) Since Acquisition	1,730
Carrying Amount at Which Carried [Abstract]
Land	2,017
Buildings and Improvements	9,800
Total	11,817
Accumulated Depreciation at December 31, 2012	3,911
Depreciable Life (Years)	40 years
650 Park Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,916
Buildings and Improvements	4,378
Net Improvements (Retirements) Since Acquisition	2,192
Carrying Amount at Which Carried [Abstract]
Land	1,916
Buildings and Improvements	6,570
Total	8,486
Accumulated Depreciation at December 31, 2012	3,122
Depreciable Life (Years)	40 years
500 North Gulph Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,303
Buildings and Improvements	5,201
Net Improvements (Retirements) Since Acquisition	1,652
Carrying Amount at Which Carried [Abstract]
Land	1,303
Buildings and Improvements	6,853
Total	8,156
Accumulated Depreciation at December 31, 2012	3,088
Depreciable Life (Years)	40 years
741 First Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,287
Buildings and Improvements	5,151
Net Improvements (Retirements) Since Acquisition	12
Carrying Amount at Which Carried [Abstract]
Land	1,287
Buildings and Improvements	5,162
Total	6,450
Accumulated Depreciation at December 31, 2012	2,117
Depreciable Life (Years)	40 years
875 First Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	618
Buildings and Improvements	2,473
Net Improvements (Retirements) Since Acquisition	3,239
Carrying Amount at Which Carried [Abstract]
Land	618
Buildings and Improvements	5,712
Total	6,330
Accumulated Depreciation at December 31, 2012	2,688
Depreciable Life (Years)	40 years
751-761 Fifth Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,097
Buildings and Improvements	4,391
Net Improvements (Retirements) Since Acquisition	31
Carrying Amount at Which Carried [Abstract]
Land	1,097
Buildings and Improvements	4,422
Total	5,519
Accumulated Depreciation at December 31, 2012	1,813
Depreciable Life (Years)	40 years
600 Park Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,012
Buildings and Improvements	4,048
Net Improvements (Retirements) Since Acquisition	385
Carrying Amount at Which Carried [Abstract]
Land	1,012
Buildings and Improvements	4,434
Total	5,445
Accumulated Depreciation at December 31, 2012	1,804
Depreciable Life (Years)	40 years
620 Allendale Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,020
Buildings and Improvements	3,839
Net Improvements (Retirements) Since Acquisition	503
Carrying Amount at Which Carried [Abstract]
Land	1,020
Buildings and Improvements	4,342
Total	5,362
Accumulated Depreciation at December 31, 2012	1,776
Depreciable Life (Years)	40 years
660 Allendale Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	396
Buildings and Improvements	948
Net Improvements (Retirements) Since Acquisition	2,898
Carrying Amount at Which Carried [Abstract]
Land	1,085
Buildings and Improvements	3,156
Total	4,242
Accumulated Depreciation at December 31, 2012	327
Depreciable Life (Years)	40 years
640 Allendale Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	439
Buildings and Improvements	432
Net Improvements (Retirements) Since Acquisition	1,579
Carrying Amount at Which Carried [Abstract]
Land	439
Buildings and Improvements	2,012
Total	2,450
Accumulated Depreciation at December 31, 2012	643
Depreciable Life (Years)	40 years
101 Lindenwood Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	4,152
Buildings and Improvements	16,606
Net Improvements (Retirements) Since Acquisition	3,554
Carrying Amount at Which Carried [Abstract]
Land	4,152
Buildings and Improvements	20,161
Total	24,312
Accumulated Depreciation at December 31, 2012	5,712
Depreciable Life (Years)	40 years
301 Lindenwood Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,729
Buildings and Improvements	10,915
Net Improvements (Retirements) Since Acquisition	1,398
Carrying Amount at Which Carried [Abstract]
Land	2,729
Buildings and Improvements	12,313
Total	15,042
Accumulated Depreciation at December 31, 2012	3,941
Depreciable Life (Years)	40 years
300 Lindenwood Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	848
Buildings and Improvements	3,394
Net Improvements (Retirements) Since Acquisition	1,266
Carrying Amount at Which Carried [Abstract]
Land	849
Buildings and Improvements	4,659
Total	5,508
Accumulated Depreciation at December 31, 2012	1,679
Depreciable Life (Years)	40 years
1700 Paoli Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	458
Buildings and Improvements	559
Net Improvements (Retirements) Since Acquisition	3,018
Carrying Amount at Which Carried [Abstract]
Land	488
Buildings and Improvements	3,547
Total	4,035
Accumulated Depreciation at December 31, 2012	1,091
Depreciable Life (Years)	40 years
100 Lindenwood Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	473
Buildings and Improvements	1,892
Net Improvements (Retirements) Since Acquisition	188
Carrying Amount at Which Carried [Abstract]
Land	473
Buildings and Improvements	2,080
Total	2,553
Accumulated Depreciation at December 31, 2012	650
Depreciable Life (Years)	40 years
200 Lindenwood Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	324
Buildings and Improvements	1,295
Net Improvements (Retirements) Since Acquisition	339
Carrying Amount at Which Carried [Abstract]
Land	324
Buildings and Improvements	1,634
Total	1,958
Accumulated Depreciation at December 31, 2012	468
Depreciable Life (Years)	40 years
14 Campus Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,244
Buildings and Improvements	4,217
Net Improvements (Retirements) Since Acquisition	1,516
Carrying Amount at Which Carried [Abstract]
Land	2,244
Buildings and Improvements	5,733
Total	7,977
Accumulated Depreciation at December 31, 2012	2,642
Depreciable Life (Years)	40 years
11 Campus Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,112
Buildings and Improvements	4,067
Net Improvements (Retirements) Since Acquisition	740
Carrying Amount at Which Carried [Abstract]
Land	1,112
Buildings and Improvements	4,807
Total	5,919
Accumulated Depreciation at December 31, 2012	1,760
Depreciable Life (Years)	40 years
17 Campus Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,108
Buildings and Improvements	5,155
Net Improvements (Retirements) Since Acquisition	(397)
Carrying Amount at Which Carried [Abstract]
Land	1,108
Buildings and Improvements	4,758
Total	5,866
Accumulated Depreciation at December 31, 2012	1,311
Depreciable Life (Years)	40 years
15 Campus Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,164
Buildings and Improvements	3,896
Net Improvements (Retirements) Since Acquisition	229
Carrying Amount at Which Carried [Abstract]
Land	1,164
Buildings and Improvements	4,125
Total	5,289
Accumulated Depreciation at December 31, 2012	1,142
Depreciable Life (Years)	40 years
18 Campus Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	787
Buildings and Improvements	3,312
Net Improvements (Retirements) Since Acquisition	(183)
Carrying Amount at Which Carried [Abstract]
Land	787
Buildings and Improvements	3,129
Total	3,916
Accumulated Depreciation at December 31, 2012	1,421
Depreciable Life (Years)	40 years
401 Plymouth Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	6,198
Buildings and Improvements	16,131
Net Improvements (Retirements) Since Acquisition	16,100
Carrying Amount at Which Carried [Abstract]
Land	6,199
Buildings and Improvements	32,230
Total	38,429
Accumulated Depreciation at December 31, 2012	9,259
Depreciable Life (Years)	40 years
4000 Chemical Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	4,373
Buildings and Improvements	24,546
Net Improvements (Retirements) Since Acquisition	4,370
Carrying Amount at Which Carried [Abstract]
Land	4,373
Buildings and Improvements	28,916
Total	33,289
Accumulated Depreciation at December 31, 2012	5,424
Depreciable Life (Years)	40 years
610 West Germantown Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	3,651
Buildings and Improvements	14,514
Net Improvements (Retirements) Since Acquisition	3,231
Carrying Amount at Which Carried [Abstract]
Land	3,651
Buildings and Improvements	17,745
Total	21,396
Accumulated Depreciation at December 31, 2012	4,757
Depreciable Life (Years)	40 years
600 West Germantown Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	3,652
Buildings and Improvements	15,288
Net Improvements (Retirements) Since Acquisition	2,252
Carrying Amount at Which Carried [Abstract]
Land	3,652
Buildings and Improvements	17,540
Total	21,192
Accumulated Depreciation at December 31, 2012	5,361
Depreciable Life (Years)	40 years
630 West Germantown Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	3,558
Buildings and Improvements	14,743
Net Improvements (Retirements) Since Acquisition	2,204
Carrying Amount at Which Carried [Abstract]
Land	3,558
Buildings and Improvements	16,947
Total	20,505
Accumulated Depreciation at December 31, 2012	5,248
Depreciable Life (Years)	40 years
620 West Germantown Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	3,572
Buildings and Improvements	14,435
Net Improvements (Retirements) Since Acquisition	1,621
Carrying Amount at Which Carried [Abstract]
Land	3,572
Buildings and Improvements	16,056
Total	19,628
Accumulated Depreciation at December 31, 2012	4,557
Depreciable Life (Years)	40 years
660 West Germantown Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	0
Buildings and Improvements	0
Net Improvements (Retirements) Since Acquisition	11,097
Carrying Amount at Which Carried [Abstract]
Land	0
Buildings and Improvements	11,097
Total	11,097
Accumulated Depreciation at December 31, 2012	112
Depreciable Life (Years)	30 years
2240/2250 Butler Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,104
Buildings and Improvements	4,627
Net Improvements (Retirements) Since Acquisition	1,216
Carrying Amount at Which Carried [Abstract]
Land	1,104
Buildings and Improvements	5,843
Total	6,947
Accumulated Depreciation at December 31, 2012	3,075
Depreciable Life (Years)	40 years
2260 Butler Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	661
Buildings and Improvements	2,727
Net Improvements (Retirements) Since Acquisition	1,195
Carrying Amount at Which Carried [Abstract]
Land	662
Buildings and Improvements	3,922
Total	4,583
Accumulated Depreciation at December 31, 2012	1,864
Depreciable Life (Years)	40 years
120 West Germantown Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	685
Buildings and Improvements	2,773
Net Improvements (Retirements) Since Acquisition	823
Carrying Amount at Which Carried [Abstract]
Land	685
Buildings and Improvements	3,596
Total	4,281
Accumulated Depreciation at December 31, 2012	1,656
Depreciable Life (Years)	40 years
140 West Germantown Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	481
Buildings and Improvements	1,976
Net Improvements (Retirements) Since Acquisition	428
Carrying Amount at Which Carried [Abstract]
Land	482
Buildings and Improvements	2,404
Total	2,885
Accumulated Depreciation at December 31, 2012	1,198
Depreciable Life (Years)	40 years
351 Plymouth Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,043
Buildings and Improvements	555
Net Improvements (Retirements) Since Acquisition	0
Carrying Amount at Which Carried [Abstract]
Land	1,043
Buildings and Improvements	555
Total	1,598
Accumulated Depreciation at December 31, 2012	108
Depreciable Life (Years)	40 years
150 Radnor Chester Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	11,925
Buildings and Improvements	36,986
Net Improvements (Retirements) Since Acquisition	12,134
Carrying Amount at Which Carried [Abstract]
Land	11,897
Buildings and Improvements	49,148
Total	61,045
Accumulated Depreciation at December 31, 2012	14,336
Depreciable Life (Years)	29 years
One Radnor Corporate Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	7,323
Buildings and Improvements	28,613
Net Improvements (Retirements) Since Acquisition	23,071
Carrying Amount at Which Carried [Abstract]
Land	7,323
Buildings and Improvements	51,684
Total	59,007
Accumulated Depreciation at December 31, 2012	13,046
Depreciable Life (Years)	29 years
201 King of Prussia Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	8,956
Buildings and Improvements	29,811
Net Improvements (Retirements) Since Acquisition	4,762
Carrying Amount at Which Carried [Abstract]
Land	8,949
Buildings and Improvements	34,579
Total	43,529
Accumulated Depreciation at December 31, 2012	12,390
Depreciable Life (Years)	25 years
555 Lancaster Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	8,014
Buildings and Improvements	16,508
Net Improvements (Retirements) Since Acquisition	18,744
Carrying Amount at Which Carried [Abstract]
Land	8,609
Buildings and Improvements	34,657
Total	43,266
Accumulated Depreciation at December 31, 2012	11,048
Depreciable Life (Years)	24 years
Four Radnor Corporate Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	5,406
Buildings and Improvements	21,390
Net Improvements (Retirements) Since Acquisition	11,971
Carrying Amount at Which Carried [Abstract]
Land	5,705
Buildings and Improvements	33,061
Total	38,767
Accumulated Depreciation at December 31, 2012	11,026
Depreciable Life (Years)	30 years
Five Radnor Corporate Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	6,506
Buildings and Improvements	25,525
Net Improvements (Retirements) Since Acquisition	1,906
Carrying Amount at Which Carried [Abstract]
Land	6,578
Buildings and Improvements	27,359
Total	33,937
Accumulated Depreciation at December 31, 2012	6,368
Depreciable Life (Years)	38 years
Three Radnor Corporate Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	4,773
Buildings and Improvements	17,961
Net Improvements (Retirements) Since Acquisition	2,449
Carrying Amount at Which Carried [Abstract]
Land	4,791
Buildings and Improvements	20,392
Total	25,183
Accumulated Depreciation at December 31, 2012	6,212
Depreciable Life (Years)	29 years
Two Radnor Corporate Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	3,937
Buildings and Improvements	15,484
Net Improvements (Retirements) Since Acquisition	2,816
Carrying Amount at Which Carried [Abstract]
Land	3,942
Buildings and Improvements	18,295
Total	22,237
Accumulated Depreciation at December 31, 2012	5,111
Depreciable Life (Years)	29 years
130 Radnor Chester Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,573
Buildings and Improvements	8,338
Net Improvements (Retirements) Since Acquisition	3,531
Carrying Amount at Which Carried [Abstract]
Land	2,567
Buildings and Improvements	11,875
Total	14,442
Accumulated Depreciation at December 31, 2012	3,322
Depreciable Life (Years)	25 years
170 Radnor Chester Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,514
Buildings and Improvements	8,147
Net Improvements (Retirements) Since Acquisition	3,285
Carrying Amount at Which Carried [Abstract]
Land	2,509
Buildings and Improvements	11,437
Total	13,946
Accumulated Depreciation at December 31, 2012	3,758
Depreciable Life (Years)	25 years
101 West Elm Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	6,251
Buildings and Improvements	25,209
Net Improvements (Retirements) Since Acquisition	2,685
Carrying Amount at Which Carried [Abstract]
Land	6,251
Buildings and Improvements	27,894
Total	34,145
Accumulated Depreciation at December 31, 2012	5,524
Depreciable Life (Years)	40 years
1 West Elm Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	3,557
Buildings and Improvements	14,249
Net Improvements (Retirements) Since Acquisition	1,128
Carrying Amount at Which Carried [Abstract]
Land	3,557
Buildings and Improvements	15,377
Total	18,934
Accumulated Depreciation at December 31, 2012	3,068
Depreciable Life (Years)	40 years
595 East Swedesford Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,729
Buildings and Improvements	10,917
Net Improvements (Retirements) Since Acquisition	2,076
Carrying Amount at Which Carried [Abstract]
Land	2,729
Buildings and Improvements	12,992
Total	15,722
Accumulated Depreciation at December 31, 2012	3,441
Depreciable Life (Years)	40 years
575 East Swedesford Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,178
Buildings and Improvements	8,712
Net Improvements (Retirements) Since Acquisition	1,888
Carrying Amount at Which Carried [Abstract]
Land	2,178
Buildings and Improvements	10,600
Total	12,778
Accumulated Depreciation at December 31, 2012	3,017
Depreciable Life (Years)	40 years
565 East Swedesford Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,872
Buildings and Improvements	7,489
Net Improvements (Retirements) Since Acquisition	1,610
Carrying Amount at Which Carried [Abstract]
Land	1,872
Buildings and Improvements	9,099
Total	10,971
Accumulated Depreciation at December 31, 2012	2,435
Depreciable Life (Years)	40 years
585 East Swedesford Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,350
Buildings and Improvements	5,401
Net Improvements (Retirements) Since Acquisition	358
Carrying Amount at Which Carried [Abstract]
Land	1,350
Buildings and Improvements	5,758
Total	7,109
Accumulated Depreciation at December 31, 2012	1,536
Depreciable Life (Years)	40 years
1336 Enterprise Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	731
Buildings and Improvements	2,946
Net Improvements (Retirements) Since Acquisition	47
Carrying Amount at Which Carried [Abstract]
Land	731
Buildings and Improvements	2,993
Total	3,724
Accumulated Depreciation at December 31, 2012	1,346
Depreciable Life (Years)	40 years
2970 Market Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	197,111
Initial Cost [Abstract]
Land	22,430
Buildings and Improvements	217,763
Net Improvements (Retirements) Since Acquisition	10,375
Carrying Amount at Which Carried [Abstract]
Land	22,430
Buildings and Improvements	228,138
Total	250,568
Accumulated Depreciation at December 31, 2012	14,793
Depreciable Life (Years)	40 years
2929 Arch Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	0
Buildings and Improvements	208,570
Net Improvements (Retirements) Since Acquisition	17,566
Carrying Amount at Which Carried [Abstract]
Land	0
Buildings and Improvements	226,136
Total	226,136
Accumulated Depreciation at December 31, 2012	65,488
Depreciable Life (Years)	40 years
130 North 18th Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	14,496
Buildings and Improvements	107,736
Net Improvements (Retirements) Since Acquisition	9,692
Carrying Amount at Which Carried [Abstract]
Land	14,473
Buildings and Improvements	117,451
Total	131,924
Accumulated Depreciation at December 31, 2012	32,765
Depreciable Life (Years)	23 years
100 North 18th Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	89,340
Initial Cost [Abstract]
Land	16,066
Buildings and Improvements	100,255
Net Improvements (Retirements) Since Acquisition	5,079
Carrying Amount at Which Carried [Abstract]
Land	16,066
Buildings and Improvements	105,334
Total	121,400
Accumulated Depreciation at December 31, 2012	29,007
Depreciable Life (Years)	33 years
1717 Arch Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	0
Buildings and Improvements	98,188
Net Improvements (Retirements) Since Acquisition	14,286
Carrying Amount at Which Carried [Abstract]
Land	0
Buildings and Improvements	112,474
Total	112,474
Accumulated Depreciation at December 31, 2012	7,266
Depreciable Life (Years)	40 years
2930 Chestnut Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	42,303
Initial Cost [Abstract]
Land	0
Buildings and Improvements	76,008
Net Improvements (Retirements) Since Acquisition	2,570
Carrying Amount at Which Carried [Abstract]
Land	0
Buildings and Improvements	78,578
Total	78,578
Accumulated Depreciation at December 31, 2012	4,576
Depreciable Life (Years)	40 years
1900 Market [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	7,768
Buildings and Improvements	17,263
Net Improvements (Retirements) Since Acquisition	1
Carrying Amount at Which Carried [Abstract]
Land	7,768
Buildings and Improvements	17,264
Total	25,032
Accumulated Depreciation at December 31, 2012	52
Depreciable Life (Years)	30 years
3020 Market Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	0
Buildings and Improvements	21,417
Net Improvements (Retirements) Since Acquisition	310
Carrying Amount at Which Carried [Abstract]
Land	0
Buildings and Improvements	21,727
Total	21,727
Accumulated Depreciation at December 31, 2012	1,177
Depreciable Life (Years)	26 years
101-103 Juniper Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	0
Buildings and Improvements	14,401
Net Improvements (Retirements) Since Acquisition	283
Carrying Amount at Which Carried [Abstract]
Land	0
Buildings and Improvements	14,684
Total	14,684
Accumulated Depreciation at December 31, 2012	578
Depreciable Life (Years)	40 years
Philadelphia Marine Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	532
Buildings and Improvements	2,196
Net Improvements (Retirements) Since Acquisition	3,175
Carrying Amount at Which Carried [Abstract]
Land	628
Buildings and Improvements	5,275
Total	5,903
Accumulated Depreciation at December 31, 2012	1,943
Depreciable Life (Years)	40 years
11720 Beltsville Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	3,831
Buildings and Improvements	16,661
Net Improvements (Retirements) Since Acquisition	3,916
Carrying Amount at Which Carried [Abstract]
Land	3,904
Buildings and Improvements	20,504
Total	24,408
Accumulated Depreciation at December 31, 2012	4,991
Depreciable Life (Years)	46 years
11700 Beltsville Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,808
Buildings and Improvements	12,081
Net Improvements (Retirements) Since Acquisition	161
Carrying Amount at Which Carried [Abstract]
Land	2,863
Buildings and Improvements	12,187
Total	15,050
Accumulated Depreciation at December 31, 2012	2,131
Depreciable Life (Years)	46 years
11710 Beltsville Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,278
Buildings and Improvements	11,100
Net Improvements (Retirements) Since Acquisition	(814)
Carrying Amount at Which Carried [Abstract]
Land	2,321
Buildings and Improvements	10,243
Total	12,564
Accumulated Depreciation at December 31, 2012	1,821
Depreciable Life (Years)	46 years
6600 Rockledge Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	0
Buildings and Improvements	37,421
Net Improvements (Retirements) Since Acquisition	11,158
Carrying Amount at Which Carried [Abstract]
Land	0
Buildings and Improvements	48,579
Total	48,579
Accumulated Depreciation at December 31, 2012	10,486
Depreciable Life (Years)	50 years
11740 Beltsville Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	198
Buildings and Improvements	870
Net Improvements (Retirements) Since Acquisition	42
Carrying Amount at Which Carried [Abstract]
Land	202
Buildings and Improvements	908
Total	1,111
Accumulated Depreciation at December 31, 2012	168
Depreciable Life (Years)	46 years
12015 Lee Jackson Memorial Highway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	3,770
Buildings and Improvements	22,895
Net Improvements (Retirements) Since Acquisition	3,042
Carrying Amount at Which Carried [Abstract]
Land	3,842
Buildings and Improvements	25,866
Total	29,707
Accumulated Depreciation at December 31, 2012	4,930
Depreciable Life (Years)	42 years
11781 Lee Jackson Memorial Highway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	3,246
Buildings and Improvements	19,836
Net Improvements (Retirements) Since Acquisition	(886)
Carrying Amount at Which Carried [Abstract]
Land	3,307
Buildings and Improvements	18,889
Total	22,196
Accumulated Depreciation at December 31, 2012	3,580
Depreciable Life (Years)	40 years
4401 Fair Lakes Court [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,569
Buildings and Improvements	11,982
Net Improvements (Retirements) Since Acquisition	224
Carrying Amount at Which Carried [Abstract]
Land	1,599
Buildings and Improvements	12,177
Total	13,776
Accumulated Depreciation at December 31, 2012	1,925
Depreciable Life (Years)	52 years
3141 Fairview Park Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	22,000
Initial Cost [Abstract]
Land	5,918
Buildings and Improvements	40,981
Net Improvements (Retirements) Since Acquisition	10,297
Carrying Amount at Which Carried [Abstract]
Land	7,081
Buildings and Improvements	50,116
Total	57,196
Accumulated Depreciation at December 31, 2012	7,598
Depreciable Life (Years)	51 years
2340 Dulles Corner Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	16,345
Buildings and Improvements	65,379
Net Improvements (Retirements) Since Acquisition	18,364
Carrying Amount at Which Carried [Abstract]
Land	16,129
Buildings and Improvements	83,959
Total	100,088
Accumulated Depreciation at December 31, 2012	21,130
Depreciable Life (Years)	40 years
2291 Wood Oak Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	8,243
Buildings and Improvements	52,413
Net Improvements (Retirements) Since Acquisition	13,489
Carrying Amount at Which Carried [Abstract]
Land	8,782
Buildings and Improvements	65,364
Total	74,145
Accumulated Depreciation at December 31, 2012	9,097
Depreciable Life (Years)	55 years
2355 Dulles Corner Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	10,365
Buildings and Improvements	43,876
Net Improvements (Retirements) Since Acquisition	4,585
Carrying Amount at Which Carried [Abstract]
Land	10,365
Buildings and Improvements	48,462
Total	58,826
Accumulated Depreciation at December 31, 2012	9,474
Depreciable Life (Years)	40 years
2251 Corporate Park Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	11,472
Buildings and Improvements	45,893
Net Improvements (Retirements) Since Acquisition	717
Carrying Amount at Which Carried [Abstract]
Land	11,472
Buildings and Improvements	46,610
Total	58,082
Accumulated Depreciation at December 31, 2012	7,131
Depreciable Life (Years)	40 years
196/198 Van Buren Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	7,931
Buildings and Improvements	43,812
Net Improvements (Retirements) Since Acquisition	6,076
Carrying Amount at Which Carried [Abstract]
Land	8,348
Buildings and Improvements	49,471
Total	57,819
Accumulated Depreciation at December 31, 2012	8,695
Depreciable Life (Years)	53 years
2411 Dulles Corner Park [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	7,279
Buildings and Improvements	46,340
Net Improvements (Retirements) Since Acquisition	3,712
Carrying Amount at Which Carried [Abstract]
Land	7,417
Buildings and Improvements	49,915
Total	57,331
Accumulated Depreciation at December 31, 2012	9,208
Depreciable Life (Years)	50 years
2121 Cooperative Way [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	5,598
Buildings and Improvements	38,639
Net Improvements (Retirements) Since Acquisition	2,193
Carrying Amount at Which Carried [Abstract]
Land	5,795
Buildings and Improvements	40,635
Total	46,430
Accumulated Depreciation at December 31, 2012	5,685
Depreciable Life (Years)	54 years
13880 Dulles Corner Lane [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	7,236
Buildings and Improvements	39,213
Net Improvements (Retirements) Since Acquisition	(1,132)
Carrying Amount at Which Carried [Abstract]
Land	7,373
Buildings and Improvements	37,944
Total	45,317
Accumulated Depreciation at December 31, 2012	5,598
Depreciable Life (Years)	55 years
2201 Cooperative Way [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	4,809
Buildings and Improvements	34,093
Net Improvements (Retirements) Since Acquisition	1,476
Carrying Amount at Which Carried [Abstract]
Land	4,809
Buildings and Improvements	35,569
Total	40,378
Accumulated Depreciation at December 31, 2012	4,856
Depreciable Life (Years)	54 years
13825 Sunrise Valley Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	3,794
Buildings and Improvements	19,365
Net Improvements (Retirements) Since Acquisition	368
Carrying Amount at Which Carried [Abstract]
Land	3,866
Buildings and Improvements	19,662
Total	23,527
Accumulated Depreciation at December 31, 2012	2,968
Depreciable Life (Years)	46 years
1676 International Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	60,869
Initial Cost [Abstract]
Land	18,437
Buildings and Improvements	97,538
Net Improvements (Retirements) Since Acquisition	1,698
Carrying Amount at Which Carried [Abstract]
Land	18,785
Buildings and Improvements	98,888
Total	117,673
Accumulated Depreciation at December 31, 2012	15,357
Depreciable Life (Years)	55 years
8260 Greensboro Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	32,319
Initial Cost [Abstract]
Land	7,952
Buildings and Improvements	33,964
Net Improvements (Retirements) Since Acquisition	692
Carrying Amount at Which Carried [Abstract]
Land	8,102
Buildings and Improvements	34,506
Total	42,608
Accumulated Depreciation at December 31, 2012	5,393
Depreciable Life (Years)	52 years
1880 Campus Commons Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	6,164
Buildings and Improvements	28,114
Net Improvements (Retirements) Since Acquisition	5,606
Carrying Amount at Which Carried [Abstract]
Land	6,281
Buildings and Improvements	33,603
Total	39,884
Accumulated Depreciation at December 31, 2012	4,634
Depreciable Life (Years)	52 years
2273 Research Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	5,167
Buildings and Improvements	31,110
Net Improvements (Retirements) Since Acquisition	3,334
Carrying Amount at Which Carried [Abstract]
Land	5,237
Buildings and Improvements	34,374
Total	39,611
Accumulated Depreciation at December 31, 2012	7,419
Depreciable Life (Years)	45 years
2275 Research Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	5,059
Buildings and Improvements	29,668
Net Improvements (Retirements) Since Acquisition	2,421
Carrying Amount at Which Carried [Abstract]
Land	5,154
Buildings and Improvements	31,994
Total	37,148
Accumulated Depreciation at December 31, 2012	6,500
Depreciable Life (Years)	45 years
2277 Research Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	4,649
Buildings and Improvements	26,952
Net Improvements (Retirements) Since Acquisition	1,659
Carrying Amount at Which Carried [Abstract]
Land	4,733
Buildings and Improvements	28,526
Total	33,260
Accumulated Depreciation at December 31, 2012	5,330
Depreciable Life (Years)	45 years
1900 Gallows Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	7,797
Buildings and Improvements	47,817
Net Improvements (Retirements) Since Acquisition	6,537
Carrying Amount at Which Carried [Abstract]
Land	7,944
Buildings and Improvements	54,207
Total	62,151
Accumulated Depreciation at December 31, 2012	7,639
Depreciable Life (Years)	52 years
8521 Leesburg Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	4,316
Buildings and Improvements	30,885
Net Improvements (Retirements) Since Acquisition	(713)
Carrying Amount at Which Carried [Abstract]
Land	4,397
Buildings and Improvements	30,091
Total	34,488
Accumulated Depreciation at December 31, 2012	4,656
Depreciable Life (Years)	51 years
457 Haddonfield Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,142
Buildings and Improvements	9,120
Net Improvements (Retirements) Since Acquisition	1,190
Carrying Amount at Which Carried [Abstract]
Land	2,142
Buildings and Improvements	10,310
Total	12,452
Accumulated Depreciation at December 31, 2012	4,491
Depreciable Life (Years)	40 years
220 Lake Drive East [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,144
Buildings and Improvements	8,798
Net Improvements (Retirements) Since Acquisition	735
Carrying Amount at Which Carried [Abstract]
Land	2,144
Buildings and Improvements	9,533
Total	11,677
Accumulated Depreciation at December 31, 2012	2,954
Depreciable Life (Years)	40 years
200 Lake Drive East [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,069
Buildings and Improvements	8,275
Net Improvements (Retirements) Since Acquisition	1,281
Carrying Amount at Which Carried [Abstract]
Land	2,069
Buildings and Improvements	9,556
Total	11,625
Accumulated Depreciation at December 31, 2012	2,901
Depreciable Life (Years)	40 years
210 Lake Drive East [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,645
Buildings and Improvements	6,579
Net Improvements (Retirements) Since Acquisition	1,067
Carrying Amount at Which Carried [Abstract]
Land	1,645
Buildings and Improvements	7,646
Total	9,291
Accumulated Depreciation at December 31, 2012	2,288
Depreciable Life (Years)	40 years
6 East Clementon Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,345
Buildings and Improvements	5,366
Net Improvements (Retirements) Since Acquisition	682
Carrying Amount at Which Carried [Abstract]
Land	1,345
Buildings and Improvements	6,048
Total	7,393
Accumulated Depreciation at December 31, 2012	2,498
Depreciable Life (Years)	40 years
20 East Clementon Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	769
Buildings and Improvements	3,055
Net Improvements (Retirements) Since Acquisition	499
Carrying Amount at Which Carried [Abstract]
Land	769
Buildings and Improvements	3,554
Total	4,323
Accumulated Depreciation at December 31, 2012	1,460
Depreciable Life (Years)	40 years
10 Foster Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	244
Buildings and Improvements	971
Net Improvements (Retirements) Since Acquisition	113
Carrying Amount at Which Carried [Abstract]
Land	244
Buildings and Improvements	1,084
Total	1,328
Accumulated Depreciation at December 31, 2012	476
Depreciable Life (Years)	40 years
7 Foster Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	231
Buildings and Improvements	921
Net Improvements (Retirements) Since Acquisition	91
Carrying Amount at Which Carried [Abstract]
Land	231
Buildings and Improvements	1,011
Total	1,243
Accumulated Depreciation at December 31, 2012	400
Depreciable Life (Years)	40 years
50 East Clementon Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	114
Buildings and Improvements	964
Net Improvements (Retirements) Since Acquisition	3
Carrying Amount at Which Carried [Abstract]
Land	114
Buildings and Improvements	967
Total	1,081
Accumulated Depreciation at December 31, 2012	406
Depreciable Life (Years)	40 years
2 Foster Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	185
Buildings and Improvements	730
Net Improvements (Retirements) Since Acquisition	16
Carrying Amount at Which Carried [Abstract]
Land	185
Buildings and Improvements	746
Total	931
Accumulated Depreciation at December 31, 2012	316
Depreciable Life (Years)	40 years
4 Foster Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	183
Buildings and Improvements	726
Net Improvements (Retirements) Since Acquisition	5
Carrying Amount at Which Carried [Abstract]
Land	183
Buildings and Improvements	732
Total	914
Accumulated Depreciation at December 31, 2012	307
Depreciable Life (Years)	40 years
1 Foster Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	93
Buildings and Improvements	364
Net Improvements (Retirements) Since Acquisition	76
Carrying Amount at Which Carried [Abstract]
Land	93
Buildings and Improvements	440
Total	533
Accumulated Depreciation at December 31, 2012	202
Depreciable Life (Years)	40 years
5 U.S. Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	21
Buildings and Improvements	81
Net Improvements (Retirements) Since Acquisition	3
Carrying Amount at Which Carried [Abstract]
Land	21
Buildings and Improvements	84
Total	105
Accumulated Depreciation at December 31, 2012	35
Depreciable Life (Years)	40 years
5 Foster Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	9
Buildings and Improvements	32
Net Improvements (Retirements) Since Acquisition	26
Carrying Amount at Which Carried [Abstract]
Land	9
Buildings and Improvements	58
Total	67
Accumulated Depreciation at December 31, 2012	25
Depreciable Life (Years)	40 years
1009 Lenox Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	4,876
Buildings and Improvements	19,284
Net Improvements (Retirements) Since Acquisition	3,866
Carrying Amount at Which Carried [Abstract]
Land	5,118
Buildings and Improvements	22,909
Total	28,026
Accumulated Depreciation at December 31, 2012	9,337
Depreciable Life (Years)	40 years
989 Lenox Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	3,701
Buildings and Improvements	14,802
Net Improvements (Retirements) Since Acquisition	1,494
Carrying Amount at Which Carried [Abstract]
Land	3,850
Buildings and Improvements	16,147
Total	19,997
Accumulated Depreciation at December 31, 2012	4,038
Depreciable Life (Years)	40 years
2000 Lenox Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,291
Buildings and Improvements	12,221
Net Improvements (Retirements) Since Acquisition	2,384
Carrying Amount at Which Carried [Abstract]
Land	2,684
Buildings and Improvements	14,212
Total	16,896
Accumulated Depreciation at December 31, 2012	4,097
Depreciable Life (Years)	40 years
1200 Lenox Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,071
Buildings and Improvements	12,967
Net Improvements (Retirements) Since Acquisition	2,500
Carrying Amount at Which Carried [Abstract]
Land	1,071
Buildings and Improvements	15,467
Total	16,538
Accumulated Depreciation at December 31, 2012	2,656
Depreciable Life (Years)	40 years
997 Lenox Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,410
Buildings and Improvements	9,700
Net Improvements (Retirements) Since Acquisition	4,323
Carrying Amount at Which Carried [Abstract]
Land	2,540
Buildings and Improvements	13,893
Total	16,433
Accumulated Depreciation at December 31, 2012	5,267
Depreciable Life (Years)	40 years
993 Lenox Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,811
Buildings and Improvements	17,996
Net Improvements (Retirements) Since Acquisition	(4,571)
Carrying Amount at Which Carried [Abstract]
Land	2,960
Buildings and Improvements	13,276
Total	16,236
Accumulated Depreciation at December 31, 2012	5,124
Depreciable Life (Years)	40 years
100 Lenox Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	0
Buildings and Improvements	0
Net Improvements (Retirements) Since Acquisition	12,114
Carrying Amount at Which Carried [Abstract]
Land	1,134
Buildings and Improvements	10,980
Total	12,114
Accumulated Depreciation at December 31, 2012	2,471
Depreciable Life (Years)	40 years
1000 Lenox Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,174
Buildings and Improvements	4,696
Net Improvements (Retirements) Since Acquisition	2,180
Carrying Amount at Which Carried [Abstract]
Land	1,244
Buildings and Improvements	6,806
Total	8,050
Accumulated Depreciation at December 31, 2012	2,999
Depreciable Life (Years)	40 years
1120 Executive Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,074
Buildings and Improvements	8,415
Net Improvements (Retirements) Since Acquisition	1,971
Carrying Amount at Which Carried [Abstract]
Land	2,074
Buildings and Improvements	10,386
Total	12,460
Accumulated Depreciation at December 31, 2012	4,540
Depreciable Life (Years)	40 years
Two Eves Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	818
Buildings and Improvements	3,461
Net Improvements (Retirements) Since Acquisition	278
Carrying Amount at Which Carried [Abstract]
Land	818
Buildings and Improvements	3,738
Total	4,557
Accumulated Depreciation at December 31, 2012	1,713
Depreciable Life (Years)	40 years
Five Eves Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	703
Buildings and Improvements	2,819
Net Improvements (Retirements) Since Acquisition	582
Carrying Amount at Which Carried [Abstract]
Land	703
Buildings and Improvements	3,401
Total	4,104
Accumulated Depreciation at December 31, 2012	1,520
Depreciable Life (Years)	40 years
Four B Eves Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	588
Buildings and Improvements	2,369
Net Improvements (Retirements) Since Acquisition	348
Carrying Amount at Which Carried [Abstract]
Land	588
Buildings and Improvements	2,717
Total	3,305
Accumulated Depreciation at December 31, 2012	1,224
Depreciable Life (Years)	40 years
Four A Eves Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	539
Buildings and Improvements	2,168
Net Improvements (Retirements) Since Acquisition	137
Carrying Amount at Which Carried [Abstract]
Land	539
Buildings and Improvements	2,305
Total	2,844
Accumulated Depreciation at December 31, 2012	1,081
Depreciable Life (Years)	40 years
308 Harper Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,643
Buildings and Improvements	6,663
Net Improvements (Retirements) Since Acquisition	1,070
Carrying Amount at Which Carried [Abstract]
Land	1,644
Buildings and Improvements	7,732
Total	9,376
Accumulated Depreciation at December 31, 2012	2,993
Depreciable Life (Years)	40 years
700 East Gate Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	3,569
Buildings and Improvements	14,436
Net Improvements (Retirements) Since Acquisition	2,094
Carrying Amount at Which Carried [Abstract]
Land	3,569
Buildings and Improvements	16,530
Total	20,099
Accumulated Depreciation at December 31, 2012	6,720
Depreciable Life (Years)	40 years
10000 Midlantic Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	3,206
Buildings and Improvements	12,857
Net Improvements (Retirements) Since Acquisition	2,066
Carrying Amount at Which Carried [Abstract]
Land	3,206
Buildings and Improvements	14,923
Total	18,129
Accumulated Depreciation at December 31, 2012	6,542
Depreciable Life (Years)	40 years
15000 Midlantic Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	3,061
Buildings and Improvements	12,254
Net Improvements (Retirements) Since Acquisition	1,403
Carrying Amount at Which Carried [Abstract]
Land	3,061
Buildings and Improvements	13,657
Total	16,718
Accumulated Depreciation at December 31, 2012	5,770
Depreciable Life (Years)	40 years
1000 Atrium Way [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,061
Buildings and Improvements	8,180
Net Improvements (Retirements) Since Acquisition	5,015
Carrying Amount at Which Carried [Abstract]
Land	2,061
Buildings and Improvements	13,195
Total	15,256
Accumulated Depreciation at December 31, 2012	5,540
Depreciable Life (Years)	40 years
1000 Howard Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,297
Buildings and Improvements	9,288
Net Improvements (Retirements) Since Acquisition	3,015
Carrying Amount at Which Carried [Abstract]
Land	2,297
Buildings and Improvements	12,303
Total	14,600
Accumulated Depreciation at December 31, 2012	4,712
Depreciable Life (Years)	40 years
2000 Midlantic Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,202
Buildings and Improvements	8,823
Net Improvements (Retirements) Since Acquisition	1,898
Carrying Amount at Which Carried [Abstract]
Land	2,203
Buildings and Improvements	10,720
Total	12,923
Accumulated Depreciation at December 31, 2012	4,236
Depreciable Life (Years)	40 years
701 East Gate Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,736
Buildings and Improvements	6,877
Net Improvements (Retirements) Since Acquisition	1,480
Carrying Amount at Which Carried [Abstract]
Land	1,736
Buildings and Improvements	8,358
Total	10,093
Accumulated Depreciation at December 31, 2012	3,094
Depreciable Life (Years)	40 years
9000 Midlantic Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,472
Buildings and Improvements	5,895
Net Improvements (Retirements) Since Acquisition	1,830
Carrying Amount at Which Carried [Abstract]
Land	1,472
Buildings and Improvements	7,725
Total	9,197
Accumulated Depreciation at December 31, 2012	2,919
Depreciable Life (Years)	40 years
307 Fellowship Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,565
Buildings and Improvements	6,342
Net Improvements (Retirements) Since Acquisition	1,226
Carrying Amount at Which Carried [Abstract]
Land	1,565
Buildings and Improvements	7,568
Total	9,133
Accumulated Depreciation at December 31, 2012	2,891
Depreciable Life (Years)	40 years
309 Fellowship Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,518
Buildings and Improvements	6,154
Net Improvements (Retirements) Since Acquisition	596
Carrying Amount at Which Carried [Abstract]
Land	1,518
Buildings and Improvements	6,750
Total	8,268
Accumulated Depreciation at December 31, 2012	2,702
Depreciable Life (Years)	40 years
303 Fellowship Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,493
Buildings and Improvements	6,055
Net Improvements (Retirements) Since Acquisition	638
Carrying Amount at Which Carried [Abstract]
Land	1,494
Buildings and Improvements	6,692
Total	8,186
Accumulated Depreciation at December 31, 2012	2,652
Depreciable Life (Years)	40 years
305 Fellowship Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,421
Buildings and Improvements	5,768
Net Improvements (Retirements) Since Acquisition	978
Carrying Amount at Which Carried [Abstract]
Land	1,421
Buildings and Improvements	6,745
Total	8,167
Accumulated Depreciation at December 31, 2012	2,661
Depreciable Life (Years)	40 years
1000 Bishops Gate [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	934
Buildings and Improvements	6,287
Net Improvements (Retirements) Since Acquisition	413
Carrying Amount at Which Carried [Abstract]
Land	934
Buildings and Improvements	6,700
Total	7,634
Accumulated Depreciation at December 31, 2012	2,028
Depreciable Life (Years)	40 years
161 Gaither Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,016
Buildings and Improvements	4,064
Net Improvements (Retirements) Since Acquisition	654
Carrying Amount at Which Carried [Abstract]
Land	1,016
Buildings and Improvements	4,718
Total	5,734
Accumulated Depreciation at December 31, 2012	1,602
Depreciable Life (Years)	40 years
4000 Midlantic Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	714
Buildings and Improvements	5,085
Net Improvements (Retirements) Since Acquisition	(1,819)
Carrying Amount at Which Carried [Abstract]
Land	714
Buildings and Improvements	3,265
Total	3,980
Accumulated Depreciation at December 31, 2012	1,528
Depreciable Life (Years)	40 years
815 East Gate Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	636
Buildings and Improvements	2,584
Net Improvements (Retirements) Since Acquisition	200
Carrying Amount at Which Carried [Abstract]
Land	636
Buildings and Improvements	2,783
Total	3,420
Accumulated Depreciation at December 31, 2012	1,130
Depreciable Life (Years)	40 years
817 East Gate Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	611
Buildings and Improvements	2,426
Net Improvements (Retirements) Since Acquisition	360
Carrying Amount at Which Carried [Abstract]
Land	611
Buildings and Improvements	2,785
Total	3,397
Accumulated Depreciation at December 31, 2012	1,200
Depreciable Life (Years)	40 years
400 Commerce Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,528
Buildings and Improvements	9,220
Net Improvements (Retirements) Since Acquisition	1,198
Carrying Amount at Which Carried [Abstract]
Land	2,528
Buildings and Improvements	10,418
Total	12,946
Accumulated Depreciation at December 31, 2012	3,382
Depreciable Life (Years)	40 years
100 Commerce Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,160
Buildings and Improvements	4,633
Net Improvements (Retirements) Since Acquisition	716
Carrying Amount at Which Carried [Abstract]
Land	1,160
Buildings and Improvements	5,350
Total	6,509
Accumulated Depreciation at December 31, 2012	2,209
Depreciable Life (Years)	40 years
200 Commerce Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	911
Buildings and Improvements	4,414
Net Improvements (Retirements) Since Acquisition	1,018
Carrying Amount at Which Carried [Abstract]
Land	911
Buildings and Improvements	5,432
Total	6,343
Accumulated Depreciation at December 31, 2012	1,844
Depreciable Life (Years)	40 years
Main Street-Plaza 1000 [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,732
Buildings and Improvements	10,942
Net Improvements (Retirements) Since Acquisition	3,402
Carrying Amount at Which Carried [Abstract]
Land	2,732
Buildings and Improvements	14,344
Total	17,076
Accumulated Depreciation at December 31, 2012	6,730
Depreciable Life (Years)	40 years
Main Street-Piazza [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	696
Buildings and Improvements	2,802
Net Improvements (Retirements) Since Acquisition	28
Carrying Amount at Which Carried [Abstract]
Land	696
Buildings and Improvements	2,831
Total	3,526
Accumulated Depreciation at December 31, 2012	1,269
Depreciable Life (Years)	40 years
Main Street-Promenade [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	531
Buildings and Improvements	2,052
Net Improvements (Retirements) Since Acquisition	339
Carrying Amount at Which Carried [Abstract]
Land	532
Buildings and Improvements	2,391
Total	2,922
Accumulated Depreciation at December 31, 2012	990
Depreciable Life (Years)	40 years
920 North King Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	6,141
Buildings and Improvements	21,140
Net Improvements (Retirements) Since Acquisition	1,083
Carrying Amount at Which Carried [Abstract]
Land	6,141
Buildings and Improvements	22,223
Total	28,364
Accumulated Depreciation at December 31, 2012	6,120
Depreciable Life (Years)	30 years
300 Delaware Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	6,368
Buildings and Improvements	13,739
Net Improvements (Retirements) Since Acquisition	2,615
Carrying Amount at Which Carried [Abstract]
Land	6,369
Buildings and Improvements	16,354
Total	22,722
Accumulated Depreciation at December 31, 2012	5,432
Depreciable Life (Years)	23 years
Two Righter Parkway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,802
Buildings and Improvements	11,217
Net Improvements (Retirements) Since Acquisition	6,190
Carrying Amount at Which Carried [Abstract]
Land	2,802
Buildings and Improvements	17,407
Total	20,209
Accumulated Depreciation at December 31, 2012	3,253
Depreciable Life (Years)	40 years
One Righter Parkway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,545
Buildings and Improvements	10,195
Net Improvements (Retirements) Since Acquisition	4,478
Carrying Amount at Which Carried [Abstract]
Land	2,545
Buildings and Improvements	14,673
Total	17,218
Accumulated Depreciation at December 31, 2012	7,235
Depreciable Life (Years)	40 years
4364 South Alston Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,622
Buildings and Improvements	6,419
Net Improvements (Retirements) Since Acquisition	844
Carrying Amount at Which Carried [Abstract]
Land	1,581
Buildings and Improvements	7,304
Total	8,885
Accumulated Depreciation at December 31, 2012	2,712
Depreciable Life (Years)	40 years
4805 Lake Brooke Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,640
Buildings and Improvements	6,567
Net Improvements (Retirements) Since Acquisition	1,661
Carrying Amount at Which Carried [Abstract]
Land	1,640
Buildings and Improvements	8,227
Total	9,868
Accumulated Depreciation at December 31, 2012	3,496
Depreciable Life (Years)	40 years
Overlook II [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	748
Buildings and Improvements	4,492
Net Improvements (Retirements) Since Acquisition	147
Carrying Amount at Which Carried [Abstract]
Land	791
Buildings and Improvements	4,595
Total	5,386
Accumulated Depreciation at December 31, 2012	444
Depreciable Life (Years)	40 years
Overlook I [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	748
Buildings and Improvements	3,976
Net Improvements (Retirements) Since Acquisition	149
Carrying Amount at Which Carried [Abstract]
Land	791
Buildings and Improvements	4,081
Total	4,872
Accumulated Depreciation at December 31, 2012	406
Depreciable Life (Years)	40 years
2812 Emerywood Parkway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,069
Buildings and Improvements	4,281
Net Improvements (Retirements) Since Acquisition	1,048
Carrying Amount at Which Carried [Abstract]
Land	1,069
Buildings and Improvements	5,329
Total	6,398
Accumulated Depreciation at December 31, 2012	2,342
Depreciable Life (Years)	40 years
300 Arboretum Place [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	5,450
Buildings and Improvements	21,892
Net Improvements (Retirements) Since Acquisition	3,707
Carrying Amount at Which Carried [Abstract]
Land	5,450
Buildings and Improvements	25,599
Total	31,049
Accumulated Depreciation at December 31, 2012	10,276
Depreciable Life (Years)	40 years
7501 Boulders View Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	4,669
Buildings and Improvements	19,699
Net Improvements (Retirements) Since Acquisition	2,057
Carrying Amount at Which Carried [Abstract]
Land	4,925
Buildings and Improvements	21,500
Total	26,425
Accumulated Depreciation at December 31, 2012	3,285
Depreciable Life (Years)	40 years
7300 Beaufont Springs Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	4,672
Buildings and Improvements	19,689
Net Improvements (Retirements) Since Acquisition	1,517
Carrying Amount at Which Carried [Abstract]
Land	4,922
Buildings and Improvements	20,956
Total	25,878
Accumulated Depreciation at December 31, 2012	2,858
Depreciable Life (Years)	40 years
6800 Paragon Place [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	4,552
Buildings and Improvements	18,414
Net Improvements (Retirements) Since Acquisition	1,918
Carrying Amount at Which Carried [Abstract]
Land	4,552
Buildings and Improvements	20,332
Total	24,884
Accumulated Depreciation at December 31, 2012	3,705
Depreciable Life (Years)	40 years
6802 Paragon Place [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,917
Buildings and Improvements	11,454
Net Improvements (Retirements) Since Acquisition	2,644
Carrying Amount at Which Carried [Abstract]
Land	2,917
Buildings and Improvements	14,098
Total	17,015
Accumulated Depreciation at December 31, 2012	4,032
Depreciable Life (Years)	40 years
1025 Boulders Parkway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,574
Buildings and Improvements	11,297
Net Improvements (Retirements) Since Acquisition	1,390
Carrying Amount at Which Carried [Abstract]
Land	2,824
Buildings and Improvements	12,437
Total	15,261
Accumulated Depreciation at December 31, 2012	1,770
Depreciable Life (Years)	40 years
2100-2116 West Laburnam Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,482
Buildings and Improvements	8,846
Net Improvements (Retirements) Since Acquisition	3,046
Carrying Amount at Which Carried [Abstract]
Land	2,482
Buildings and Improvements	11,892
Total	14,374
Accumulated Depreciation at December 31, 2012	4,783
Depreciable Life (Years)	40 years
7401 Beaufont Springs Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,349
Buildings and Improvements	10,396
Net Improvements (Retirements) Since Acquisition	921
Carrying Amount at Which Carried [Abstract]
Land	2,599
Buildings and Improvements	11,067
Total	13,666
Accumulated Depreciation at December 31, 2012	1,545
Depreciable Life (Years)	40 years
7325 Beaufont Springs Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,344
Buildings and Improvements	10,377
Net Improvements (Retirements) Since Acquisition	503
Carrying Amount at Which Carried [Abstract]
Land	2,594
Buildings and Improvements	10,630
Total	13,224
Accumulated Depreciation at December 31, 2012	1,470
Depreciable Life (Years)	40 years
9011 Arboretum Parkway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,857
Buildings and Improvements	7,702
Net Improvements (Retirements) Since Acquisition	871
Carrying Amount at Which Carried [Abstract]
Land	1,857
Buildings and Improvements	8,573
Total	10,430
Accumulated Depreciation at December 31, 2012	3,324
Depreciable Life (Years)	40 years
6806 Paragon Place [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	0
Buildings and Improvements	10,288
Net Improvements (Retirements) Since Acquisition	106
Carrying Amount at Which Carried [Abstract]
Land	403
Buildings and Improvements	9,992
Total	10,394
Accumulated Depreciation at December 31, 2012	2,185
Depreciable Life (Years)	40 years
9100 Arboretum Parkway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,362
Buildings and Improvements	5,489
Net Improvements (Retirements) Since Acquisition	669
Carrying Amount at Which Carried [Abstract]
Land	1,362
Buildings and Improvements	6,158
Total	7,520
Accumulated Depreciation at December 31, 2012	2,359
Depreciable Life (Years)	40 years
2511 Brittons Hill Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,202
Buildings and Improvements	4,820
Net Improvements (Retirements) Since Acquisition	1,472
Carrying Amount at Which Carried [Abstract]
Land	1,202
Buildings and Improvements	6,292
Total	7,494
Accumulated Depreciation at December 31, 2012	2,698
Depreciable Life (Years)	40 years
100 Gateway Centre Parkway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	391
Buildings and Improvements	5,410
Net Improvements (Retirements) Since Acquisition	511
Carrying Amount at Which Carried [Abstract]
Land	391
Buildings and Improvements	5,921
Total	6,312
Accumulated Depreciation at December 31, 2012	1,595
Depreciable Life (Years)	40 years
9200 Arboretum Parkway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	985
Buildings and Improvements	3,973
Net Improvements (Retirements) Since Acquisition	1,242
Carrying Amount at Which Carried [Abstract]
Land	985
Buildings and Improvements	5,216
Total	6,200
Accumulated Depreciation at December 31, 2012	1,931
Depreciable Life (Years)	40 years
9210 Arboretum Parkway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,110
Buildings and Improvements	4,474
Net Improvements (Retirements) Since Acquisition	527
Carrying Amount at Which Carried [Abstract]
Land	1,110
Buildings and Improvements	5,001
Total	6,111
Accumulated Depreciation at December 31, 2012	1,997
Depreciable Life (Years)	40 years
2201-2245 Tomlynn Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,020
Buildings and Improvements	4,067
Net Improvements (Retirements) Since Acquisition	685
Carrying Amount at Which Carried [Abstract]
Land	1,020
Buildings and Improvements	4,752
Total	5,772
Accumulated Depreciation at December 31, 2012	1,780
Depreciable Life (Years)	40 years
9211 Arboretum Parkway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	582
Buildings and Improvements	2,433
Net Improvements (Retirements) Since Acquisition	827
Carrying Amount at Which Carried [Abstract]
Land	582
Buildings and Improvements	3,261
Total	3,842
Accumulated Depreciation at December 31, 2012	1,053
Depreciable Life (Years)	40 years
2212-2224 Tomlynn Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	502
Buildings and Improvements	2,014
Net Improvements (Retirements) Since Acquisition	364
Carrying Amount at Which Carried [Abstract]
Land	502
Buildings and Improvements	2,378
Total	2,880
Accumulated Depreciation at December 31, 2012	857
Depreciable Life (Years)	40 years
2244 Dabney Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	550
Buildings and Improvements	2,203
Net Improvements (Retirements) Since Acquisition	37
Carrying Amount at Which Carried [Abstract]
Land	550
Buildings and Improvements	2,240
Total	2,790
Accumulated Depreciation at December 31, 2012	892
Depreciable Life (Years)	40 years
2221-2245 Dabney Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	530
Buildings and Improvements	2,123
Net Improvements (Retirements) Since Acquisition	73
Carrying Amount at Which Carried [Abstract]
Land	530
Buildings and Improvements	2,196
Total	2,726
Accumulated Depreciation at December 31, 2012	857
Depreciable Life (Years)	40 years
2248 Dabney Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	512
Buildings and Improvements	2,049
Net Improvements (Retirements) Since Acquisition	132
Carrying Amount at Which Carried [Abstract]
Land	512
Buildings and Improvements	2,181
Total	2,693
Accumulated Depreciation at December 31, 2012	835
Depreciable Life (Years)	40 years
2277 Dabney Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	507
Buildings and Improvements	2,034
Net Improvements (Retirements) Since Acquisition	61
Carrying Amount at Which Carried [Abstract]
Land	507
Buildings and Improvements	2,095
Total	2,602
Accumulated Depreciation at December 31, 2012	811
Depreciable Life (Years)	40 years
2246 Dabney Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	455
Buildings and Improvements	1,822
Net Improvements (Retirements) Since Acquisition	18
Carrying Amount at Which Carried [Abstract]
Land	455
Buildings and Improvements	1,840
Total	2,295
Accumulated Depreciation at December 31, 2012	726
Depreciable Life (Years)	40 years
2161-2179 Tomlynn Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	423
Buildings and Improvements	1,695
Net Improvements (Retirements) Since Acquisition	100
Carrying Amount at Which Carried [Abstract]
Land	423
Buildings and Improvements	1,795
Total	2,218
Accumulated Depreciation at December 31, 2012	697
Depreciable Life (Years)	40 years
2130-2146 Tomlynn Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	353
Buildings and Improvements	1,416
Net Improvements (Retirements) Since Acquisition	354
Carrying Amount at Which Carried [Abstract]
Land	353
Buildings and Improvements	1,769
Total	2,123
Accumulated Depreciation at December 31, 2012	750
Depreciable Life (Years)	40 years
2251 Dabney Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	387
Buildings and Improvements	1,552
Net Improvements (Retirements) Since Acquisition	153
Carrying Amount at Which Carried [Abstract]
Land	387
Buildings and Improvements	1,705
Total	2,092
Accumulated Depreciation at December 31, 2012	703
Depreciable Life (Years)	40 years
2256 Dabney Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	356
Buildings and Improvements	1,427
Net Improvements (Retirements) Since Acquisition	218
Carrying Amount at Which Carried [Abstract]
Land	356
Buildings and Improvements	1,645
Total	2,001
Accumulated Depreciation at December 31, 2012	684
Depreciable Life (Years)	40 years
2120 Tomlynn Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	281
Buildings and Improvements	1,125
Net Improvements (Retirements) Since Acquisition	196
Carrying Amount at Which Carried [Abstract]
Land	281
Buildings and Improvements	1,321
Total	1,602
Accumulated Depreciation at December 31, 2012	525
Depreciable Life (Years)	40 years
2240 Dabney Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	264
Buildings and Improvements	1,059
Net Improvements (Retirements) Since Acquisition	11
Carrying Amount at Which Carried [Abstract]
Land	264
Buildings and Improvements	1,069
Total	1,333
Accumulated Depreciation at December 31, 2012	422
Depreciable Life (Years)	40 years
Boulders Land [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,256
Buildings and Improvements	0
Net Improvements (Retirements) Since Acquisition	28
Carrying Amount at Which Carried [Abstract]
Land	1,259
Buildings and Improvements	25
Total	1,284
Accumulated Depreciation at December 31, 2012	0
5900 & 5950 La Place Court [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	3,706
Buildings and Improvements	11,185
Net Improvements (Retirements) Since Acquisition	3,123
Carrying Amount at Which Carried [Abstract]
Land	3,954
Buildings and Improvements	14,059
Total	18,014
Accumulated Depreciation at December 31, 2012	2,451
Depreciable Life (Years)	48 years
5963 La Place Court [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,824
Buildings and Improvements	9,413
Net Improvements (Retirements) Since Acquisition	2,069
Carrying Amount at Which Carried [Abstract]
Land	2,998
Buildings and Improvements	11,307
Total	14,306
Accumulated Depreciation at December 31, 2012	1,840
Depreciable Life (Years)	55 years
5973 Avenida Encinas [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,121
Buildings and Improvements	8,361
Net Improvements (Retirements) Since Acquisition	1,433
Carrying Amount at Which Carried [Abstract]
Land	2,255
Buildings and Improvements	9,659
Total	11,915
Accumulated Depreciation at December 31, 2012	1,942
Depreciable Life (Years)	45 years
2035 Corte Del Nogal [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	3,261
Buildings and Improvements	6,077
Net Improvements (Retirements) Since Acquisition	1,140
Carrying Amount at Which Carried [Abstract]
Land	3,498
Buildings and Improvements	6,980
Total	10,478
Accumulated Depreciation at December 31, 2012	1,656
Depreciable Life (Years)	39 years
1200 Concord Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	6,395
Buildings and Improvements	24,664
Net Improvements (Retirements) Since Acquisition	708
Carrying Amount at Which Carried [Abstract]
Land	6,514
Buildings and Improvements	25,251
Total	31,766
Accumulated Depreciation at December 31, 2012	5,438
Depreciable Life (Years)	34 years
1220 Concord Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	6,476
Buildings and Improvements	24,966
Net Improvements (Retirements) Since Acquisition	156
Carrying Amount at Which Carried [Abstract]
Land	6,475
Buildings and Improvements	25,122
Total	31,597
Accumulated Depreciation at December 31, 2012	5,130
Depreciable Life (Years)	34 years
155 Grand Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	13,556
Buildings and Improvements	54,266
Net Improvements (Retirements) Since Acquisition	5,016
Carrying Amount at Which Carried [Abstract]
Land	13,555
Buildings and Improvements	59,284
Total	72,839
Accumulated Depreciation at December 31, 2012	9,841
Depreciable Life (Years)	40 years
Two Kaiser Plaza [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	7,841
Buildings and Improvements	0
Net Improvements (Retirements) Since Acquisition	0
Carrying Amount at Which Carried [Abstract]
Land	7,840
Buildings and Improvements	0
Total	7,841
Accumulated Depreciation at December 31, 2012	0
Oakland Lot B [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	4,342
Buildings and Improvements	0
Net Improvements (Retirements) Since Acquisition	0
Carrying Amount at Which Carried [Abstract]
Land	4,341
Buildings and Improvements	0
Total	4,342
Accumulated Depreciation at December 31, 2012	0
16870 W Bernardo Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	2,979
Buildings and Improvements	15,896
Net Improvements (Retirements) Since Acquisition	1,762
Carrying Amount at Which Carried [Abstract]
Land	3,153
Buildings and Improvements	17,484
Total	20,638
Accumulated Depreciation at December 31, 2012	2,871
Depreciable Life (Years)	56 years
1250 Capital of Texas Hwy South [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	5,152
Buildings and Improvements	37,928
Net Improvements (Retirements) Since Acquisition	6,240
Carrying Amount at Which Carried [Abstract]
Land	5,249
Buildings and Improvements	44,072
Total	49,321
Accumulated Depreciation at December 31, 2012	8,644
Depreciable Life (Years)	52 years
1301 Mopac Expressway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	4,188
Buildings and Improvements	41,229
Net Improvements (Retirements) Since Acquisition	(761)
Carrying Amount at Which Carried [Abstract]
Land	4,249
Buildings and Improvements	40,407
Total	44,657
Accumulated Depreciation at December 31, 2012	5,765
Depreciable Life (Years)	55 years
1601 Mopac Expressway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	3,538
Buildings and Improvements	34,346
Net Improvements (Retirements) Since Acquisition	871
Carrying Amount at Which Carried [Abstract]
Land	3,604
Buildings and Improvements	35,149
Total	38,754
Accumulated Depreciation at December 31, 2012	5,512
Depreciable Life (Years)	54 years
7400 West at Lantana [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	4,651
Buildings and Improvements	20,897
Net Improvements (Retirements) Since Acquisition	1
Carrying Amount at Which Carried [Abstract]
Land	4,650
Buildings and Improvements	20,898
Total	25,549
Accumulated Depreciation at December 31, 2012	0
Depreciable Life (Years)	40 years
3711 South Mopac Expressway - II [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,688
Buildings and Improvements	19,229
Net Improvements (Retirements) Since Acquisition	4,317
Carrying Amount at Which Carried [Abstract]
Land	1,687
Buildings and Improvements	23,546
Total	25,233
Accumulated Depreciation at December 31, 2012	4,807
Depreciable Life (Years)	40 years
3711 South Mopac Expressway - I [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	1,688
Buildings and Improvements	21,011
Net Improvements (Retirements) Since Acquisition	2,464
Carrying Amount at Which Carried [Abstract]
Land	1,687
Buildings and Improvements	23,477
Total	25,163
Accumulated Depreciation at December 31, 2012	3,395
Depreciable Life (Years)	40 years
1501 South Mopac Expressway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	3,698
Buildings and Improvements	34,912
Net Improvements (Retirements) Since Acquisition	(2,190)
Carrying Amount at Which Carried [Abstract]
Land	3,767
Buildings and Improvements	32,653
Total	36,419
Accumulated Depreciation at December 31, 2012	4,556
Depreciable Life (Years)	53 years
1221 Mopac Expressway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances at December 31, 2012	0
Initial Cost [Abstract]
Land	3,291
Buildings and Improvements	31,548
Net Improvements (Retirements) Since Acquisition	5,411
Carrying Amount at Which Carried [Abstract]
Land	3,368
Buildings and Improvements	36,882
Total	40,249
Accumulated Depreciation at December 31, 2012	$ 5,169
Depreciable Life (Years)	55 years