Condensed Consolidated Statements of Equity (Unaudited) (USD $) In Thousands, except Share data, 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 Income (Loss) [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	2,950,000	36,443,000
Net income	0	0	0	26,571	0	3,132	29,703
Changes in fair value of cash flow hedges and amortization of settlement swaps	0	0	0	0	2,524	141	2,665
Changes in fair value of marketable securities	0	0	0	0	130	8	138
Issuance of common stock under:
Stock option and restricted stock plans	0	0	1,956	0	0	0	1,956
Stock option and restricted stock plans shares (in shares)	0	16,000
Sale of common stock	0	0	122,905	0	0	0	122,905
Sale of common stock (in shares)	0	817,000					817,445
Equity based compensation costs	0	0	(256)	0	0	575	319
Distributions to noncontrolling interest	0	0	0	0	0	(3,995)	(3,995)
Redemptions of noncontrolling interest	0	0	0	0	0	(1,329)	(1,329)
Common and preferred stock dividends	0	0	0	(46,496)	0	0	(46,496)
Reversal of unrealized gains upon the sale of marketable securities	0	0	0	0	(1,673)	(94)	(1,767)
Balances at Mar. 31, 2013	$ 73,750	$ 3	$ 2,329,383	$ (464,391)	$ (68,280)	$ 113,750	$ 1,984,215
Balances (in shares) at Mar. 31, 2013	2,950,000	37,276,000