Real Estate Partnerships (Summarized Operating Results and Financial Position of Partnership) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
Real Estate Partnerships Operating Results [Line Items]
Revenue	$ 157,947	$ 147,560	$ 315,699	$ 293,849
Depreciation and amortization	39,853	35,199	80,477	71,770
Interest expense	27,147	28,733	54,552	57,526
NET INCOME	38,797	33,596	74,639	77,718
Our share of net income from real estate partnership	372	438	684	739
Real estate, net	3,664,996		3,664,996		3,555,379
Cash	108,366	82,774	108,366	82,774	36,988	67,806
TOTAL ASSETS	4,085,203		4,085,203		3,898,565
Mortgages payable	724,984		724,984		760,789
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	4,085,203		4,085,203		3,898,565
Our investment in real estate partnership	33,029		33,029		33,169
Federal / Lion Venture LP [Member]
Real Estate Partnerships Operating Results [Line Items]
Revenue	4,624	4,709	9,573	9,298
Other operating expenses	1,318	1,228	3,135	2,567
Depreciation and amortization	1,361	1,375	2,730	2,751
Interest expense	841	844	1,683	1,689
Total expenses	3,520	3,447	7,548	7,007
NET INCOME	1,104	1,262	2,025	2,291
Our share of net income from real estate partnership	372	438	684	796
Real estate, net	172,602		172,602		174,509
Cash	3,990		3,990		2,735
Other assets	5,413		5,413		5,536
TOTAL ASSETS	182,005		182,005		182,780
Mortgages payable	57,040		57,040		57,155
Other liabilities	4,397		4,397		4,771
Partners' capital	120,568		120,568		120,854
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	182,005		182,005		182,780
Our share of unconsolidated debt	17,112		17,112		17,147
Our investment in real estate partnership	$ 33,029		$ 33,029		$ 33,169