Condensed Consolidated Statements of Stockholders' Equity, Noncontrolling Interest, and Comprehensive Income (Unaudited) (USD $) In Thousands, except Share data	Total	Series F Preferred stock	Series H Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Distributions in Excess of Net Income [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interest [Member]
Balances at December 31, 2010 at Dec. 31, 2010	$ 1,355,014	$ 25,000	$ 0	$ 3	$ 1,515,468	$ (313,308)	$ (77,217)	$ 205,068
Balances (in shares) at Dec. 31, 2010 at Dec. 31, 2010		1,000,000		31,325,000
Comprehensive income:
Net income	28,560	0	0	0	0	22,709	0	5,851
Reversal of unrealized gains upon the sale of marketable securities	(4,402)	0	0	0	0	0	(4,109)	(293)
Change in fair value of cash flow hedges and amortization of swap settlements	4,743	0	0	0	0	0	4,431	312
Change in fair value of marketable securities	2,119	0	0	0	0	0	1,977	142
Comprehensive income (loss)	31,020
Issuance of common stock under:
Stock option and restricted stock plans (in shares)				87,000
Stock option and restricted stock plans	6,540	0	0	0	6,540	0	0	0
Sale of common stock (in shares)				1,312,000
Sale of common stock	168,592	0	0	0	168,592	0	0	0
Equity based compensation costs	560	0	0	0	0	0	0	560
Equity related issuance costs	(652)	0	0	0	(652)	0	0	0
Issuance of Series H Preferred (in shares)			2,950,000
Issuance of Series H Preferred	71,427	0	73,750	0	(2,323)	0	0	0
Redemption of Series F Preferred (in shares)		(1,000,000)
Redemption of Series F Preferred	(25,000)	(25,000)	0	0	0	0	0	0
Contributions from noncontrolling interest	800	0	0		0	0	0	800
Distributions to noncontrolling interest	(9,667)	0	0	0	0	0	0	(9,667)
Dividends declared	(69,063)	0	0	0	0	(69,063)	0	0
Redemption of Series B Preferred (in shares)					1,200,000
Redemption of Series B Preferred	(78,800)	0	0	0		0	0	(80,000)
Redemptions of noncontrolling interest	(4,019)	0	0	0	(1,134)	0	0	(2,885)
Balances at June 30, 2011 at Jun. 30, 2011	$ 1,446,752	$ 0	$ 73,750	$ 3	$ 1,687,691	$ (359,662)	$ (74,918)	$ 119,888
Balance (in shares) at June 30, 2011 at Jun. 30, 2011		0	2,950,000	32,724,000