Condensed Consolidated Statements of Equity (Unaudited) (USD $) In Thousands, unless otherwise specified	Series H Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Distributions in Excess of Accumulated Earnings [Member]	Accumulated Other Comprehensive Loss, Net [Member]	Noncontrolling Interest [Member]	Total
Balances at Dec. 31, 2012	$ 73,750	$ 3	$ 2,204,778	$ (444,466)	$ (69,261)	$ 115,312	$ 1,880,116
Balances (in shares) at Dec. 31, 2012	2,950	36,443
Net income	0	0	0	52,885	0	6,393	59,278
Reversal of unrealized gains upon the sale of marketable securities	0	0	0	0	(1,673)	(94)	(1,767)
Change in fair value of cash flow hedges and amortization of swap settlements	0	0	0	0	8,551	486	9,037
Changes in fair value of marketable securities	0	0	0	0	(430)	(24)	(454)
Issuance of common stock under:
Stock option and restricted stock plans	0	0	5,308	0	0	0	5,308
Stock option and restricted stock plans shares (in shares)	0	58
Sale of common stock	0	0	122,905	0	0	0	122,905
Sale of common stock (in shares)	0	817
Equity based compensation costs	0	0	(615)	0	0	1,098	483
Distributions to noncontrolling interest	0	0	0	0	0	(9,811)	(9,811)
Redemptions of noncontrolling interest	0	0	(546)	0	0	(1,471)	(2,017)
Common and preferred stock dividends	0	0	0	(93,034)	0	0	(93,034)
Balances at Jun. 30, 2013	$ 73,750	$ 3	$ 2,331,830	$ (484,615)	$ (62,813)	$ 111,889	$ 1,970,044
Balances (in shares) at Jun. 30, 2013	2,950	37,318