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, 2014		14,000,000
Common Stock, Shares, Outstanding at Dec. 31, 2014			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	(77)			(77)			(77)
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	2,146			1,867			1,868	278
Distributions on Common Shares and Units	(22,932)					(22,860)	(22,860)	(72)
Distributions on Preferred Shares	(6,488)					(6,488)	(6,488)
Unrealized gain (loss) on derivative instruments	(4,169)				(4,169)		(4,169)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	7,170					7,143	7,143	27
Preferred Stock, Shares Outstanding at Mar. 31, 2015		14,000,000
Common Stock, Shares, Outstanding at Mar. 31, 2015			71,735,129
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Mar. 31, 2015	$ 1,754,339	$ 140	$ 717	1,862,807	(4,510)	(106,368)	1,752,786	1,553
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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
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	1,841			1,562			1,565	276
Distributions on Common Shares and Units	(27,762)					(27,672)	(27,672)	(90)
Distributions on Preferred Shares	(5,844)					(5,844)	(5,844)
Unrealized gain (loss) on derivative instruments	(11,484)				(11,484)		(11,484)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 16,637					16,579	16,579	58
Preferred Stock, Shares Outstanding at Mar. 31, 2016	8,400,000	8,400,000
Common Stock, Shares, Outstanding at Mar. 31, 2016	71,922,904		71,922,904
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Mar. 31, 2016	$ 1,592,307	$ 84	$ 719	$ 1,731,920	$ (16,234)	$ (126,871)	$ 1,589,618	$ 2,689