Real Estate Partnerships (Summarized Operating Results and Financial Position of Partnership) (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010	Dec. 31, 2009
Revenue	$ 137,664	$ 133,446	$ 411,593	$ 404,463
Depreciation and amortization	32,068	29,431	94,355	89,224
Interest expense	23,795	25,299	72,744	76,679
NET INCOME	48,302	31,010	117,157	93,932
Income from real estate partnerships	434	125	1,201	506
Real estate, net	2,921,626		2,921,626		2,860,738
Cash	22,070	9,174	22,070	9,174	15,797	135,389
TOTAL ASSETS	3,254,848		3,254,848		3,159,553
Mortgages payable	484,502		484,502		529,501
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	3,254,848		3,254,848		3,159,553
Our investment in real estate partnership	57,828		57,828		51,606
Federal / Lion Venture LP [Member]
Revenue	4,743	4,510	14,387	13,688
Other operating expenses	1,276	1,322	4,260	4,664
Depreciation and amortization	1,296	1,259	3,864	3,771
Interest expense	846	849	2,542	2,551
Total expenses	3,418	3,430	10,666	10,986
NET INCOME	1,325	1,080	3,721	2,702
Income from real estate partnerships	452	355	1,253	901
Real estate, net	178,585		178,585		181,565
Cash	4,678		4,678		3,054
Other assets	6,268		6,268		7,336
TOTAL ASSETS	189,531		189,531		191,955
Mortgages payable	57,429		57,429		57,584
Other liabilities	4,825		4,825		5,439
Partners' capital	127,277		127,277		128,932
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	189,531		189,531		191,955
Our share of unconsolidated debt	17,229		17,229		17,275
Our investment in real estate partnership	$ 35,028		$ 35,028		$ 35,504