Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Preferred Shares [Member]	Common Shares [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Distributions in Excess of Retained Earnings [Member]	Parent [Member]	Noncontrolling Interest [Member]
Preferred Stock, Shares Outstanding at Dec. 31, 2012		9,000,000
Common Stock, Shares, Outstanding at Dec. 31, 2012			60,955,090
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
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
Preferred Stock, Shares Outstanding at Dec. 31, 2013		13,000,000
Common Stock, Shares, Outstanding at Dec. 31, 2013			63,709,628
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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares, net of offering costs, Shares		1,000,000	7,530,000
Issuance of shares, net of offering costs, Value	316,910	$ 10	$ 75	316,825			316,910
Issuance of Common Shares for Board Of Trustees Compensation , Shares			13,793
Issuance of Common Shares for Board Of Trustees Compensation, Value	421			421			421
Repurchase of Common Stock, Shares			(20,539)
Repurchase of Common Shares, Value	(632)			(632)			(632)
Share-based Compensation, Shares			62,498
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures			$ 1
Share-based Compensation, Value	11,695			9,085			9,086	2,609
Distributions on Common Shares and Units	(62,857)					(62,298)	(62,298)	(559)
Distributions on Preferred Shares	(25,095)					(25,079)	(25,079)	(16)
Redemption of non-controlling interest LTIP units, Shares			258,101
Redemption of non-controlling interest LTIP units, Value	(5,231)		$ 3	(2,098)			(2,095)	(3,136)
Unrealized gain (loss) on derivative instruments	(1,427)				(1,427)		(1,427)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 73,543					72,866	72,866	677
Preferred Stock, Shares Outstanding at Dec. 31, 2014	14,000,000	14,000,000
Common Stock, Shares, Outstanding at Dec. 31, 2014	71,553,481		71,553,481
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Dec. 31, 2014	$ 1,782,411	$ 140	$ 716	1,864,739	(341)	(84,163)	1,781,091	1,320
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares, net of offering costs, Value	(195)			(195)			(195)
Issuance of Common Shares for Board Of Trustees Compensation , Shares			8,084
Issuance of Common Shares for Board Of Trustees Compensation, Value	372			372			372
Repurchase of Common Stock, Shares			(84,835)
Repurchase of Common Shares, Value	(4,094)			(4,094)			(4,094)
Share-based Compensation, Shares			258,399
Share-based Compensation, Value	8,331		$ 1	7,225			7,226	1,105
Distributions on Common Shares and Units	(90,612)					(90,320)	(90,320)	(292)
Distributions on Preferred Shares	(25,965)					(25,950)	(25,950)	(15)
Unrealized gain (loss) on derivative instruments	(4,409)				(4,409)		(4,409)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 94,995					94,668	94,668	327
Preferred Stock, Shares Outstanding at Dec. 31, 2015	14,000,000	14,000,000
Common Stock, Shares, Outstanding at Dec. 31, 2015	71,735,129		71,735,129
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Dec. 31, 2015	$ 1,760,834	$ 140	$ 717	$ 1,868,047	$ (4,750)	$ (105,765)	$ 1,758,389	$ 2,445