Schedule III - Summary of Real Estate and Accumulated Depreciation (Details) (USD $) In Thousands, unless otherwise specified			12 Months Ended								12 Months Ended																																														12 Months Ended																						12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Post Street 150 [Member]	Dec. 31, 2013 29th Place [Member]	Dec. 31, 2013 Andorra [Member]	Dec. 31, 2013 Assembly Square Market Place Assembly Row [Member]	Dec. 31, 2013 THE AVENUE at White Marsh [Member]	Dec. 31, 2013 Bala Cynwyd [Member]	Dec. 31, 2013 Barracks Road [Member]	Dec. 31, 2013 Bethesda Row [Member]	Dec. 31, 2013 Bethesda Row [Member] Minimum [Member]	Dec. 31, 2013 Bethesda Row [Member] Maximum [Member]	Dec. 31, 2013 Brick Plaza [Member]	Dec. 31, 2013 Bristol [Member]	Dec. 31, 2013 Chelsea [Member]	Dec. 31, 2013 Colorado Blvd [Member]	Dec. 31, 2013 Congressional Plaza [Member]	Dec. 31, 2013 Courthouse Center [Member]	Dec. 31, 2013 Courtyard Shops [Member]	Dec. 31, 2013 Crossroads [Member]	Dec. 31, 2013 Crow Canyon [Member]	Dec. 31, 2013 Darien [Member]	Dec. 31, 2013 Dedham Plaza [Member]	Dec. 31, 2013 Del Mar Village [Member]	Dec. 31, 2013 EastBayBridge [Member]	Dec. 31, 2013 Eastgate [Member]	Dec. 31, 2013 Elllisburg Circle [Member]	Dec. 31, 2013 Escondido Promenade [Member]	Dec. 31, 2013 Falls Plaza [Member]	Dec. 31, 2013 Federal Plaza [Member]	Dec. 31, 2013 Finley Square [Member]	Dec. 31, 2013 Flourtown [Member]	Dec. 31, 2013 Fresh Meadows [Member]	Dec. 31, 2013 Friendship Ctr [Member]	Dec. 31, 2013 Gaithersburg Square [Member]	Dec. 31, 2013 Garden Market [Member]	Dec. 31, 2013 Governor Plaza [Member]	Dec. 31, 2013 Gratiot Plaza [Member]	Dec. 31, 2013 Greenwich Avenue [Member]	Dec. 31, 2013 Hauppauge [Member]	Dec. 31, 2013 Hermosa Ave [Member]	Dec. 31, 2013 Hollywood Blvd [Member]	Dec. 31, 2013 Houston Street [Member]	Dec. 31, 2013 Huntington [Member]	Dec. 31, 2013 HuntingtonSquare [Member]	Dec. 31, 2013 Idylwood Plaza [Member]	Dec. 31, 2013 Kings Court [Member]	Dec. 31, 2013 Lancaster [Member]	Dec. 31, 2013 Langhorne Square [Member]	Dec. 31, 2013 Laurel [Member]	Dec. 31, 2013 Lawrence Park [Member]	Dec. 31, 2013 Leesburg Plaza [Member]	Dec. 31, 2013 Linden Square [Member]	Dec. 31, 2013 Loehmanns Plaza [Member]	Dec. 31, 2013 Melville Mall [Member]	Dec. 31, 2013 Mercer Mall [Member]	Dec. 31, 2013 Mercer Mall [Member] Minimum [Member]	Dec. 31, 2013 Mercer Mall [Member] Maximum [Member]	Dec. 31, 2013 Mid Pike Plaza [Member]	Dec. 31, 2013 Montrose Crossing [Member]	Dec. 31, 2013 Mount Vernon [Member]	Dec. 31, 2013 Town Center of New Britain [Member]	Dec. 31, 2013 North Dartmouth [Member]	Dec. 31, 2013 Northeast [Member]	Dec. 31, 2013 North Lake Commons [Member]	Dec. 31, 2013 Old Keene Mill [Member]	Dec. 31, 2013 Old Town Center [Member]	Dec. 31, 2013 Pan Am Shopping Center [Member]	Dec. 31, 2013 Pentagon Row [Member]	Dec. 31, 2013 Perring Plaza [Member]	Dec. 31, 2013 Pike 7 [Member]	Dec. 31, 2013 Plaza El Segundo [Member]	Dec. 31, 2013 Queen Anne Plaza [Member]	Dec. 31, 2013 Quince Orchard Plaza [Member]	Dec. 31, 2013 Rockville Town Square [Member]	Dec. 31, 2013 Rollingwood Apartments [Member]	Dec. 31, 2013 Sams Park and Shop [Member]	Dec. 31, 2013 Santana Row [Member]	Dec. 31, 2013 Santana Row [Member] Minimum [Member]	Dec. 31, 2013 Santana Row [Member] Maximum [Member]	Dec. 31, 2013 Saugus [Member]	Dec. 31, 2013 Shirlington [Member]	Dec. 31, 2013 Shoppes At Nottingham Square [Member]	Dec. 31, 2013 Third Street Promenade [Member]	Dec. 31, 2013 Tower [Member]	Dec. 31, 2013 Tower Shops January 19 2011 [Member]	Dec. 31, 2013 Troy [Member]	Dec. 31, 2013 Tyson Station [Member]	Dec. 31, 2013 Westgate Mall [Member]	Dec. 31, 2013 White Marsh Plaza [Member]	Dec. 31, 2013 White Marsh Other [Member]	Dec. 31, 2013 Wildwood [Member]	Dec. 31, 2013 Willow Grove [Member]	Dec. 31, 2013 Willow Lawn [Member]	Dec. 31, 2013 Wynnewood [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 660,127	$ 832,482		$ 5,090			$ 54,120		$ 37,069				$ 27,254		$ 6,968										$ 65,190															$ 13,974								$ 4,907			$ 26,275				$ 20,653	$ 55,794				$ 77,341												$ 182,129			$ 4,524	$ 22,521						$ 6,446										$ 23,095			$ 26,777
Initial cost to company, Land	1,104,678		11,685	10,211	2,432	93,252	20,682	3,565	4,363	46,579			0	3,856	9,417	5,262	2,793	1,750	16,862	4,635	27,245	29,809	12,287	14,218	29,079	1,608	4,028	19,117	1,798	10,216	9,252	1,345	24,625	12,696	7,701	2,677	2,068	525	7,484	8,791	1,116	8,300	14,680	11,713	0	4,308	0	0	720	7,458	5,723	8,184	79,382	1,237	35,622	28,684			31,388	48,624	10,068	1,282	27,214	1,152	2,782	638	3,420	8,694	0	2,800	9,709	56,606	3,319	3,197	0	552	4,840	44,562			4,383	9,761	4,441	22,645	7,170	28,823	3,126	388	6,319	3,478	60,400	9,111	1,499	3,192	8,055
Initial cost to company, Buildings and Improvements	1,630,403		9,181	18,863	12,346	34,196	72,432	14,466	16,459	35,406			24,715	15,959	19,466	4,071	7,424	1,869	21,851	11,611	54,575	18,302	12,918	39,559	138,035	5,775	11,309	15,829	1,270	17,895	9,544	3,943	25,255	20,803	5,271	4,829	4,905	1,601	5,444	15,262	280	16,920	1,976	16,008	10,075	10,026	10,714	2,103	2,974	22,525	7,160	10,722	19,247	15,096	32,882	48,028			10,335	91,819	33,501	12,285	0	10,596	8,604	998	2,765	12,929	2,955	6,461	22,799	153,556	8,457	7,949	8,092	2,246	6,319	7,502			8,291	14,808	12,849	12,709	10,518	36,313	5,193	453	107,284	21,413	1,843	1,061	6,643	7,723	13,759
Cost Capitalized Subsequent to Acquisition	2,414,382		16,160	10,857	10,768	232,268	4,065	21,931	38,355	138,402			35,040	9,831	13,836	8,788	65,584	1,075	1,874	14,817	3,633	5	9,375	2,130	395	19,444	16,224	12,070	9,802	37,539	13,750	8,627	29,490	2,685	12,623	4,798	19,660	16,929	1,041	3,746	4,439	15,922	44,829	15,769	1,314	2,361	930	11,435	17,133	21,195	18,433	16,497	47,749	17,292	1,079	33,269			140,641	12,242	36,629	1,145	(17,846)	12,896	5,140	4,935	31,014	7,061	93,397	20,637	3,664	15,422	6,367	16,598	42,536	6,837	1,671	621,900			2,141	34,857	54	42,752	3,534	12,936	21,856	3,625	20,962	198	(26,047)	8,297	21,651	71,601	15,816
Gross amount at which carried atclose of period, Land	987,735		11,685	10,225	2,432	45,890	20,685	3,566	4,363	44,880			3,939	3,856	9,396	5,262	1,020	1,750	16,894	4,635	27,245	29,809	12,287	14,180	29,079	1,608	4,013	19,117	1,819	10,216	9,252	1,470	24,628	12,696	5,973	2,677	2,068	525	7,484	8,426	1,368	8,300	14,778	11,713	0	4,308	0	75	720	7,464	5,734	8,184	79,269	1,169	35,622	28,684			7,517	48,624	10,232	1,262	9,366	1,153	2,628	638	3,420	8,695	0	2,800	9,653	40,701	3,319	2,928	0	572	4,840	57,575			4,383	4,234	4,441	25,125	7,280	28,845	4,028	475	6,319	3,478	34,311	9,111	1,499	7,790	8,055
Gross amount at which carried atclose of period, Buildings and Improvements	4,161,728		25,341	29,706	23,114	313,826	76,494	36,396	54,814	175,507			55,816	25,790	33,323	12,859	74,781	2,944	23,693	26,428	58,208	18,307	22,293	41,727	138,430	25,219	27,548	27,899	11,051	55,434	23,294	12,445	54,742	23,488	19,622	9,627	24,565	18,530	6,485	19,373	4,467	32,842	46,707	31,777	11,389	12,387	11,644	13,463	20,107	43,714	25,582	27,219	67,109	32,456	33,961	81,297			174,847	104,061	69,966	13,450	2	23,491	13,898	5,933	33,779	19,989	96,352	27,098	26,519	184,883	14,824	24,816	50,628	9,063	7,990	616,389			10,432	55,192	12,903	52,981	13,942	49,227	26,147	3,991	128,246	21,611	1,885	9,358	28,294	74,726	29,575
Gross amount at which carried atclose of period, Total	5,149,463		37,026	39,931	25,546	359,716	97,179	39,962	59,177	220,387			59,755	29,646	42,719	18,121	75,801	4,694	40,587	31,063	85,453	48,116	34,580	55,907	167,509	26,827	31,561	47,016	12,870	65,650	32,546	13,915	79,370	36,184	25,595	12,304	26,633	19,055	13,969	27,799	5,835	41,142	61,485	43,490	11,389	16,695	11,644	13,538	20,827	51,178	31,316	35,403	146,378	33,625	69,583	109,981			182,364	152,685	80,198	14,712	9,368	24,644	16,526	6,571	37,199	28,684	96,352	29,898	36,172	225,584	18,143	27,744	50,628	9,635	12,830	673,964			14,815	59,426	17,344	78,106	21,222	78,072	30,175	4,466	134,565	25,089	36,196	18,469	29,793	82,516	37,630
Accumulated Depreciation and Amortization	$ 1,350,471		$ 15,265	$ 5,793	$ 16,170	$ 17,917	$ 19,278	$ 15,006	$ 35,487	$ 49,469			$ 40,673	$ 13,521	$ 4,483	$ 8,640	$ 45,511	$ 1,410	$ 4,694	$ 12,996	$ 13,940	$ 492	$ 12,089	$ 7,982	$ 5,000	$ 16,560	$ 16,430	$ 10,400	$ 7,313	$ 35,449	$ 15,971	$ 5,146	$ 27,977	$ 7,997	$ 15,094	$ 5,649	$ 16,032	$ 14,590	$ 3,396	$ 8,918	$ 2,189	$ 9,311	$ 26,108	$ 10,832	$ 1,281	$ 7,058	$ 7,054	$ 6,947	$ 12,435	$ 31,630	$ 22,446	$ 11,085	$ 12,920	$ 23,512	$ 6,953	$ 27,818			$ 17,833	$ 8,323	$ 23,553	$ 3,360	$ 2	$ 17,270	$ 6,488	$ 4,965	$ 18,145	$ 12,654	$ 36,418	$ 19,655	$ 13,129	$ 12,133	$ 7,989	$ 13,781	$ 10,249	$ 7,725	$ 4,319	$ 122,907			$ 5,033	$ 18,967	$ 3,062	$ 26,548	$ 6,852	$ 6,076	$ 18,065	$ 3,157	$ 29,850	$ 5,494	$ 512	$ 7,984	$ 22,080	$ 46,038	$ 17,538
Life on which depreciation in latest income statements is computed			35 years	35 years	35 years	35 years	35 years	35 years	35 years		35 years	50 years	35 years	35 years	35 years	35 years	35 years	35 years	35 years	35 years	35 years	35 years	35 years	35 years	35 years	35 years	35 years	35 years	25 years	35 years	35 years	35 years	35 years	35 years	35 years	35 years	35 years	25 years 9 months	35 years	35 years	35 years	35 years	35 years	35 years	35 years	35 years	26 years	22 years	35 years	35 years	22 years	35 years	35 years	35 years	35 years		25 years	35 years	50 years	35 years	35 years	35 years		35 years	35 years	33 years 4 months	35 years	35 years	35 years	35 years	35 years	35 years	35 years	35 years	50 years	25 years	35 years		40 years	50 years	35 years	35 years	35 years	35 years	35 years	35 years	22 years	17 years	35 years	35 years	35 years	33 years 4 months	35 years	35 years	35 years