Real Estate Partnerships (Summarized Operating Results and Financial Position of Partnership) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011
Real Estate Partnerships Operating Results [Line Items]
Revenue	$ 157,752	$ 146,289
Depreciation and amortization	40,624	36,571
Interest expense	27,405	28,793
NET INCOME	35,842	44,122
Our share of net income from real estate partnership	312	301
Real estate, net	3,567,385		3,555,379
Cash	31,274	69,182	36,988	67,806
TOTAL ASSETS	3,905,932		3,898,565
Mortgages payable	747,978		760,789
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	3,905,932		3,898,565
Our investment in real estate partnership	33,131		33,169
Federal / Lion Venture LP [Member]
Real Estate Partnerships Operating Results [Line Items]
Revenue	4,949	4,589
Other operating expenses	1,817	1,339
Depreciation and amortization	1,369	1,376
Interest expense	842	845
Total expenses	4,028	3,560
NET INCOME	921	1,029
Our share of net income from real estate partnership	312	358
Real estate, net	173,356		174,509
Cash	3,745		2,735
Other assets	4,924		5,536
TOTAL ASSETS	182,025		182,780
Mortgages payable	57,098		57,155
Other liabilities	3,914		4,771
Partners' capital	121,013		120,854
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	182,025		182,780
Our share of unconsolidated debt	17,130		17,147
Our investment in real estate partnership	$ 33,131		$ 33,169