CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total USD ($)	Shares of preferred stock	Shares of common stock	Preferred stock and paid in capital USD ($)	Common stock and paid in capital USD ($)	Distributions in excess of net income USD ($)
Balance at Dec. 31, 2009	$ 1,488,009			$ 337,790	$ 1,629,237	$ (479,018)
Balance (in shares) at Dec. 31, 2009		13,900,000	104,286,705
Increase (Decrease) in Stockholders' Equity
Net income	130,784					130,784
Distributions paid and payable	(208,878)					(208,878)
Shares issued in stock offerings, net of offering costs of $13,773, $25,200 and $22,471 for the year ended December 31, 2012, 2011 and 2010, respectively.	432,591				432,591
Shares issued in stock offerings, net of offering costs (in shares)			13,558,500
Share-based compensation	4,459				4,459
Share-based compensation (in shares)			213,783
Balance at Dec. 31, 2010	1,846,965			337,790	2,066,287	(557,112)
Balance (in shares) at Dec. 31, 2010		13,900,000	118,058,988
Increase (Decrease) in Stockholders' Equity
Net income	157,032					157,032
Distributions paid and payable	(245,904)					(245,904)
Shares issued in stock offerings, net of offering costs of $13,773, $25,200 and $22,471 for the year ended December 31, 2012, 2011 and 2010, respectively.	489,236				489,236
Shares issued in stock offerings, net of offering costs (in shares)			14,925,000
Shares issued pursuant to dividend reinvestment and stock purchase plan, net	1,930				1,930
Shares issued pursuant to dividend reinvestment and stock purchase plan, net (in shares)			59,605
Share-based compensation	5,595				5,595
Share-based compensation (in shares)			179,745
Balance at Dec. 31, 2011	2,254,854			337,790	2,563,048	(645,984)
Balance (in shares) at Dec. 31, 2011		13,900,000	133,223,338
Increase (Decrease) in Stockholders' Equity
Net income	159,152					159,152
Distributions paid and payable	(278,133)					(278,133)
Shares issued in stock offerings, net of offering costs of $13,773, $25,200 and $22,471 for the year ended December 31, 2012, 2011 and 2010, respectively.	395,377			395,377
Shares issued in stock offerings, net of offering costs (in shares)		16,350,000
Shares issued pursuant to dividend reinvestment and stock purchase plan, net	2,051				2,051
Shares issued pursuant to dividend reinvestment and stock purchase plan, net (in shares)			55,598
Preferred shares redeemed	(127,500)			(123,804)		(3,696)
Preferred shares redeemed (in shares)		(5,100,000)
Preferred shares redeemed	(3,696)
Share-based compensation	6,993				6,993
Share-based compensation (in shares)			173,475
Balance at Dec. 31, 2012	$ 2,412,794			$ 609,363	$ 2,572,092	$ (768,661)
Balance (in shares) at Dec. 31, 2012		25,150,000	133,452,411