Consolidated Statements of Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Preferred Shares [Member]	Common Shares [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Parent [Member]	Noncontrolling Interest [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Dec. 31, 2010	$ 688,452		$ 398	$ 698,100		$ (11,586)	$ 686,912	$ 1,540
Common Stock, Shares, Outstanding at Dec. 31, 2010			39,814,760
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares, net of offering costs		9,000,000	10,925,000
Stock Issued During Period, Value, New Issues	444,023	90	110	443,823			444,023
Share Value Issued For Board Of Trustees Compensation			8,886
Share Value Issued For Board Of Trustees Compensation	182			182			182
Payments for Repurchase of Common Stock			(6,496)
Stock Repurchased During Period, Value	140			(140)			(140)
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures			22,709
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition	1,972			787			787	1,185
Dividends, Common Stock	(17,338)					(17,004)	(17,004)	(334)
Dividends, Preferred Stock	(5,914)					(5,907)	(5,907)	(7)
Non Controlling Interest, Net Contribution	(95)							(95)
Unrealized gain (loss) on derivative instruments	0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	7,093					6,894	6,894	199
Preferred Stock, Shares Outstanding		9,000,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Sep. 30, 2011	1,118,425	90	508	1,142,752		(27,603)	1,115,747	2,678
Common Stock, Shares, Outstanding at Sep. 30, 2011			50,764,859
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Dec. 31, 2011	1,116,348	90	508	1,142,905		(30,252)	1,113,251	3,097
Common Stock, Shares, Outstanding at Dec. 31, 2011	50,769,024		50,769,024
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares, net of offering costs			9,544,087
Stock Issued During Period, Value, New Issues	211,520		95	211,425			211,520
Share Value Issued For Board Of Trustees Compensation			10,361
Share Value Issued For Board Of Trustees Compensation	199			199			199
Payments for Repurchase of Common Stock			(15,595)
Stock Repurchased During Period, Value	(319)			(319)			(319)
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures			48,324
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures			1
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition	2,750			1,564			1,565	1,185
Dividends, Common Stock	(20,810)					(20,476)	(20,476)	(334)
Dividends, Preferred Stock	(13,378)					(13,369)	(13,369)	(9)
Unrealized gain (loss) on derivative instruments	(389)				(389)		(389)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	19,295					18,991	18,991	304
Preferred Stock, Shares Outstanding	9,000,000	9,000,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Sep. 30, 2012	1,315,216	90	604	1,355,774	(389)	(45,106)	1,310,973	4,243
Common Stock, Shares, Outstanding at Sep. 30, 2012	60,356,201		60,356,201
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Jun. 30, 2012
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Unrealized gain (loss) on derivative instruments	(389)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	12,105
Preferred Stock, Shares Outstanding	9,000,000	9,000,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Sep. 30, 2012	$ 1,315,216	$ 90
Common Stock, Shares, Outstanding at Sep. 30, 2012	60,356,201