Condensed Consolidated Statement of Equity (Unaudited) (USD $) In Thousands, except Share data, unless otherwise specified	Total	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]
Balances at Dec. 31, 2014	$ 6,136,068	$ 73,750	$ 6	$ 6,651,165	$ (650,797)	$ (51,452)	$ 113,396
Balances (in shares) at Dec. 31, 2014		2,950,000	63,683,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	64,753				60,677		4,076
Change in fair value of derivatives and amortization of swap settlements	(1,335)					(1,289)	(46)
Change in fair value of marketable securities	1,934					1,873	61
Issuance of common stock under:
Stock option and restricted stock plans	15,613			15,613
Stock option and restricted stock plans (in shares)			115,000
Sale of common stock	184,158			184,158
Sale of common stock (in shares)			822,000
Equity based compensation costs	1,370			613			757
Reclassification Of Noncontrolling Interest To Redeemable Noncontrolling Interest	(144)			0			(144)
Changes in the redemption value of redeemable noncontrolling interest	(1,517)			(1,517)			0
Distributions to noncontrolling interest	(3,574)			0			(3,574)
Redemptions of noncontrolling interest	(2,154)			(1,777)			(377)
Common and preferred stock dividends	(94,316)				(94,316)
Balances at Mar. 31, 2015	$ 6,300,856	$ 73,750	$ 6	$ 6,848,255	$ (684,436)	$ (50,868)	$ 114,149
Balances (in shares) at Mar. 31, 2015		2,950,000	64,620,000