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]	Non-controlling Interests [Member]
Preferred Stock, Shares Outstanding at Dec. 31, 2014		14,000,000
Common Stock, Shares, Outstanding at Dec. 31, 2014			71,553,481
Beginning balance 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	(139)			(139)			(139)
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
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures			$ 1
Share-based Compensation, Value	4,284			3,729			3,730	554
Distributions on Common Shares and Units	(45,569)					(45,422)	(45,422)	(147)
Distributions on Preferred Shares	(12,982)					(12,975)	(12,975)	(7)
Unrealized gain (loss) on derivative instruments	(92)				(92)		(92)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	33,753					33,634	33,634	119
Preferred Stock, Shares Outstanding at Jun. 30, 2015		14,000,000
Common Stock, Shares, Outstanding at Jun. 30, 2015			71,735,129
Ending balance at Jun. 30, 2015	$ 1,757,944	$ 140	$ 717	1,864,607	(433)	(108,926)	1,756,105	1,839
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
Beginning balance at Dec. 31, 2015	$ 1,760,834	$ 140	$ 717	1,868,047	(4,750)	(105,765)	1,758,389	2,445
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Issued During Period, Shares, New Issues		5,000,000	0
Issuance of shares, net of offering costs, Value	120,969	$ 50	$ 0	120,919			120,969
Stock Redeemed or Called During Period, Shares		(5,600,000)
Stock Redeemed or Called During Period, Value	(140,025)	$ (56)		(135,800)		(4,169)	(140,025)
Issuance of Common Shares for Board Of Trustees Compensation , Shares			21,407
Issuance of Common Shares for Board Of Trustees Compensation, Value	606			606			606
Repurchase of Common Stock, Shares			(88,510)
Repurchase of Common Shares, Value	(2,496)		$ (1)	(2,495)			(2,496)
Share-based Compensation, Shares			254,878
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures			$ 3
Share-based Compensation, Value	3,901			3,346			3,349	552
Distributions on Common Shares and Units	(55,525)					(55,346)	(55,346)	(179)
Distributions on Preferred Shares	(10,094)					(10,085)	(10,085)	(9)
Unrealized gain (loss) on derivative instruments	(16,119)				(16,119)		(16,119)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 91,075					90,769	90,769	306
Preferred Stock, Shares Outstanding at Jun. 30, 2016	13,400,000	13,400,000
Common Stock, Shares, Outstanding at Jun. 30, 2016	71,922,904		71,922,904
Ending balance at Jun. 30, 2016	$ 1,753,126	$ 134	$ 719	$ 1,854,623	$ (20,869)	$ (84,596)	$ 1,750,011	$ 3,115