Consolidated Statements of Equity (Unaudited) (USD $) In Thousands, except Share data	Total	Preferred Stock	Common stock	Common Stock Additional Paid-in Capital	Common Stock Distributions in Excess of Earnings	Total Stockholders' Equity	Noncontrolling Interests - Common Units of the Operating Partnership
Beginning Balance at Dec. 31, 2009	$ 883,838	$ 121,582	$ 431	$ 913,657	$ (180,722)	$ 854,948	$ 28,890
Beginning Balance, shares at Dec. 31, 2009			43,148,762
Net income	10,833				10,701	10,701	132
Issuance of common stock (Note 7)	299,847		92	299,755		299,847
Issuance of common stock, shares (Note 7)			9,200,000
Issuance of share-based compensation awards, shares (Note 9)			3,239
Issuance of share-based compensation awards (Note 9)	1,660			1,660		1,660
Noncash amortization of share-based compensation	3,361			3,361		3,361
Exercise of stock options	83			83		83
Exercise of stock options, shares			4,000
Repurchase of common stock and restricted stock units (Note9)	(2,121)			(2,121)		(2,121)
Repurchase of common stock and restricted stock units,share (Note9)			(59,782)
Allocation to the equity component of cash paid upon repurchase of 3.25% Exchangeable Notes	(2,694)			(2,694)		(2,694)
Adjustment for noncontrolling interest				(4,985)		(4,985)	4,985
Preferred distributions and dividends	(7,598)				(7,598)	(7,598)
Dividends declared per common share and common unit ($0.70 per share/ unit)	(35,143)				(33,936)	(33,936)	(1,207)
Ending Balance at Jun. 30, 2010	1,152,066	121,582	523	1,208,716	(211,555)	1,119,266	32,800
Ending Balance, shares at Jun. 30, 2010			52,296,219
Beginning Balance at Dec. 31, 2010	1,117,730	121,582	523	1,211,498	(247,252)	1,086,351	31,379
Beginning Balance, shares at Dec. 31, 2010	52,349,670		52,349,670
Net income	8,339				8,315	8,315	24
Issuance of common stock (Note 7)	221,015		61	220,954		221,015
Issuance of common stock, shares (Note 7)	6,037,500		6,037,500
Issuance of share-based compensation awards, shares (Note 9)			68,727
Issuance of share-based compensation awards (Note 9)	2,156		1	2,155		2,156
Noncash amortization of share-based compensation	2,813			2,813		2,813
Exercise of stock options	395			395		395
Exercise of stock options, shares			15,000
Repurchase of common stock and restricted stock units (Note9)	(732)			(732)		(732)
Repurchase of common stock and restricted stock units,share (Note9)			(11,485)
Exchange of common units of the Operating Partnership				91		91	(91)
Exchange of common units of the Operating Partnership, shares			5,000
Adjustment for noncontrolling interest				(3,223)		(3,223)	3,223
Preferred distributions and dividends	(7,598)				(7,598)	(7,598)
Dividends declared per common share and common unit ($0.70 per share/ unit)	(40,585)				(39,381)	(39,381)	(1,204)
Ending Balance at Jun. 30, 2011	$ 1,303,533	$ 121,582	$ 585	$ 1,433,951	$ (285,916)	$ 1,270,202	$ 33,331
Ending Balance, shares at Jun. 30, 2011	58,464,412		58,464,412