Consolidated Statements of Equity (Unaudited) (USD $) In Thousands, except Share data, unless otherwise specified	Total	Total Stockholders' Equity	Preferred Stock [Member]	Common Stock [Member]	Common Stock Additional Paid-in Capital	Common Stock Distributions in Excess of Earnings	Noncontrolling Interests - Common Units of the Operating Partnership
Beginning Balance at Dec. 31, 2010	$ 1,117,730	$ 1,086,351	$ 121,582	$ 523	$ 1,211,498	$ (247,252)	$ 31,379
Beginning Balance, shares at Dec. 31, 2010				52,349,670
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	4,867	4,833				4,833	34
Original issuance costs of preferred stock called for redemption (Note 7)	0
Redeemable Preferred Stock, Value, Including Distributions in Excess of Earnings	0
Issuance of share-based compensation awards (Note 10)	1,875	1,875		1	1,874
Issuance of share-based compensation awards, shares (Note 10)				66,208
Noncash amortization of share-based compensation (Note 10)	1,420	1,420			1,420
Repurchase of common stock and restricted stock units (Note 10)	(732)	(732)			(732)
Repurchase of common stock and restricted stock units, shares (Note 10)				(11,485)
Exercise of stock options	395	395			395
Exercise of stock options, shares				15,000
Adjustment for noncontrolling interest	0	8			8		(8)
Preferred distributions and dividends	(3,799)	(3,799)				(3,799)
Dividends declared per common share and common unit ($0.35 per share/ unit)	(19,233)	(18,630)				(18,630)	(603)
Ending Balance at Mar. 31, 2011	1,102,523	1,071,721	121,582	524	1,214,463	(264,848)	30,802
Ending Balance, shares at Mar. 31, 2011				52,419,393
Beginning Balance at Dec. 31, 2011	1,327,482	1,293,717	121,582	588	1,448,997	(277,450)	33,765
Beginning Balance, shares at Dec. 31, 2011	58,819,717			58,819,717
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	78,671	76,876				76,876	1,795
Issuance of Series G Preferred Stock (Note 7)	96,155	96,155	96,155
Redeemable Preferred Stock, Value, Excluding Distributions in Excess of Earnings			(121,582)
Original issuance costs of preferred stock called for redemption (Note 7)	(4,918)					(4,918)
Redeemable Preferred Stock, Value, Including Distributions in Excess of Earnings	(126,500)	(126,500)
Issuance of common stock (Note 8)	382,063	382,063		95	381,968
Issuance of common stock, shares (Note 8)				9,487,500
Issuance of share-based compensation awards (Note 10)	294	294			294
Issuance of share-based compensation awards, shares (Note 10)				59,938
Noncash amortization of share-based compensation (Note 10)	1,469	1,469			1,469
Repurchase of common stock and restricted stock units (Note 10)	(603)	(603)			(603)
Repurchase of common stock and restricted stock units, shares (Note 10)				(22,312)
Exercise of stock options	129	129			129
Exercise of stock options, shares	5,000			5,000
Adjustment for noncontrolling interest	0	(4,578)			(4,578)		4,578
Preferred distributions and dividends	(4,418)	(4,418)				(4,418)
Dividends declared per common share and common unit ($0.35 per share/ unit)	(24,892)	(24,289)				(24,289)	(603)
Ending Balance at Mar. 31, 2012	$ 1,729,850	$ 1,690,315	$ 96,155	$ 683	$ 1,827,676	$ (234,199)	$ 39,535
Ending Balance, shares at Mar. 31, 2012	68,349,843			68,349,843