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, 2013		13,000,000
Common stock, shares, outstanding at Dec. 31, 2013			63,709,628
Beginning balance 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
Share-based Compensation, Value	11,695		$ 1	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)
Stock Issued During Period, Shares, Conversion of Units			258,101
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests	(5,231)		$ 3	(2,098)			(2,095)	(3,136)
Unrealized gain (loss) on derivative instruments	(1,427)				(1,427)		(1,427)
Net income (loss)	73,543					72,866	72,866	677
Preferred stock, shares outstanding at Dec. 31, 2014		14,000,000
Common stock, shares, outstanding at Dec. 31, 2014			71,553,481
Ending 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, Shares		0	0
Issuance of shares, net of offering costs, Value	(195)	$ 0	$ 0	(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
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures			$ 1
Share-based Compensation, Value	8,331			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)	$ 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
Ending 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]
Issuance of shares, net of offering costs, Shares		5,000,000
Issuance of shares, net of offering costs, Value	120,808	$ 50		120,758			120,808
Stock Redeemed or Called During Period, Shares		(9,000,000)
Stock Redeemed or Called During Period, Value	(225,050)	$ (90)		(217,870)		(7,090)	(225,050)
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
Share-based Compensation, Value	8,466		$ 3	7,358			7,361	1,105
Distributions on Common Shares and Units	(110,773)					(110,414)	(110,414)	(359)
Distributions on Preferred Shares	(19,679)					(19,662)	(19,662)	(17)
Unrealized gain (loss) on derivative instruments	2,438				2,438		2,438
Net income (loss)	$ 73,962					73,704	73,704	258
Preferred stock, shares outstanding at Dec. 31, 2016	10,000,000	10,000,000
Common stock, shares, outstanding at Dec. 31, 2016	71,922,904		71,922,904
Ending balance at Dec. 31, 2016	$ 1,609,116	$ 100	$ 719	$ 1,776,404	$ (2,312)	$ (169,227)	$ 1,605,684	$ 3,432