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, Shares		9,000,000	10,925,000
Issuance of shares, net of offering costs, Value	443,888	90	110	443,688			443,888
Issuance of Common Shares for Board Of Trustees Compensation , Shares			8,886
Issuance of Common Shares for Board Of Trustees Compensation, Value	182			182			182
Repurchase of Common Stock, Shares			(6,496)
Repurchase of Common Shares, Value	(140)			(140)			(140)
Share-based Compensation, Shares			26,874
Share-based Compensation, Value	2,654			1,075			1,075	1,579
Distributions on Common Shares and Units	(23,555)					(23,109)	(23,109)	(446)
Distributions on Preferred Shares	(10,427)					(10,413)	(10,413)	(14)
Non Controlling Interest, Net Contribution	95							95
Unrealized gain (loss) on derivative instruments	0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	15,199					14,856	14,856	343
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
Preferred Stock, Shares Outstanding at Dec. 31, 2011		9,000,000
Common Stock, Shares, Outstanding at Dec. 31, 2011			50,769,024
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares, net of offering costs, Shares			9,694,087
Issuance of shares, net of offering costs, Value	214,871		97	214,774			214,871
Issuance of Common Shares for Board Of Trustees Compensation , Shares			10,361
Issuance of Common Shares for Board Of Trustees Compensation, Value	199			199			199
Repurchase of Common Stock, Shares			(15,706)
Repurchase of Common Shares, Value	(321)			(321)			(321)
Share-based Compensation, Shares			52,789
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures			1
Share-based Compensation, Value	4,215			2,635			2,636	1,579
Distributions on Common Shares and Units	(28,246)					(27,800)	(27,800)	(446)
Distributions on Preferred Shares	(17,840)					(17,825)	(17,825)	(15)
Redemption of Non-controlling Interest LTIP Units, Units			444,535
Redemption of Non-controlling Interest LTIP Units	(2,342)		4	2,157			2,161	(4,503)
Unrealized gain (loss) on derivative instruments	(300)				(300)		(300)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	26,508					26,079	26,079	429
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Dec. 31, 2012	1,313,092	90	610	1,362,349	(300)	(49,798)	1,312,951	141
Preferred Stock, Shares Outstanding at Dec. 31, 2012	9,000,000	9,000,000
Common Stock, Shares, Outstanding at Dec. 31, 2012	60,955,090		60,955,090
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares, net of offering costs, Shares		4,000,000	2,701,893
Issuance of shares, net of offering costs, Value	175,575	40	27	175,508			175,575
Issuance of Common Shares for Board Of Trustees Compensation , Shares			9,097
Issuance of Common Shares for Board Of Trustees Compensation, Value	207			207			207
Repurchase of Common Stock, Shares			(21,644)
Repurchase of Common Shares, Value	(523)			(523)			(523)
Share-based Compensation, Shares			65,192
Share-based Compensation, Value	5,222			3,597			3,597	1,625
Distributions on Common Shares and Units	(40,099)					(39,819)	(39,819)	(280)
Distributions on Preferred Shares	(22,968)					(22,953)	(22,953)	(15)
Unrealized gain (loss) on derivative instruments	1,386				1,386		1,386
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	43,192					42,918	42,918	274
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Dec. 31, 2013	$ 1,475,084	$ 130	$ 637	$ 1,541,138	$ 1,086	$ (69,652)	$ 1,473,339	$ 1,745
Preferred Stock, Shares Outstanding at Dec. 31, 2013	13,000,000	13,000,000
Common Stock, Shares, Outstanding at Dec. 31, 2013	63,709,628		63,709,628