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, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011	Dec. 31, 2010
Real Estate Partnerships Operating Results [Line Items]
Revenue	$ 147,560	$ 136,280	$ 293,849	$ 273,929
Depreciation and amortization	35,199	31,871	71,770	62,287
Interest expense	28,733	23,905	57,526	48,949
NET INCOME	33,596	36,471	77,718	68,855
Our share of net income from real estate partnership	438	444	739	767
Real estate, net	3,306,974		3,306,974		3,298,856
Cash	82,774	19,848	82,774	19,848	67,806	15,797
TOTAL ASSETS	3,680,929		3,680,929		3,666,210
Mortgages payable	733,997		733,997		747,523
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	3,680,929		3,680,929		3,666,210
Our investment in real estate partnership	34,055		34,055		34,352
Federal / Lion Venture LP [Member]
Real Estate Partnerships Operating Results [Line Items]
Revenue	4,709	4,676	9,298	9,644
Other operating expenses	1,228	1,228	2,567	2,984
Depreciation and amortization	1,375	1,290	2,751	2,568
Interest expense	844	848	1,689	1,696
Total expenses	3,447	3,366	7,007	7,248
NET INCOME	1,262	1,310	2,291	2,396
Our share of net income from real estate partnership	438	444	796	801
Real estate, net	176,485		176,485		178,693
Cash	4,501		4,501		3,035
Other assets	5,003		5,003		6,116
TOTAL ASSETS	185,989		185,989		187,844
Mortgages payable	57,267		57,267		57,376
Other liabilities	4,434		4,434		5,391
Partners' capital	124,288		124,288		125,077
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	185,989		185,989		187,844
Our share of unconsolidated debt	17,180		17,180		17,213
Our investment in real estate partnership	$ 34,055		$ 34,055		$ 34,352