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, 2015		14,000,000
Common stock, shares, outstanding at Dec. 31, 2015			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]
Issuance of shares, net of offering costs, Shares		5,000,000
Issuance of shares, net of offering costs, Value	120,969	$ 50		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)	91,075					90,769	90,769	306
Preferred stock, shares outstanding at Jun. 30, 2016		13,400,000
Common stock, shares, outstanding at Jun. 30, 2016			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
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
Beginning balance at Dec. 31, 2016	$ 1,609,116	$ 100	$ 719	1,776,404	(2,312)	(169,227)	1,605,684	3,432
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		$ 0	$ 0
Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs	(62)			(62)			(62)
Issuance of Common Shares for Board Of Trustees Compensation , Shares			16,711
Issuance of Common Shares for Board Of Trustees Compensation, Value	503		$ 1	502			503
Repurchase of Common Stock, Shares			(3,331,478)
Repurchase of Common Shares, Value	(95,863)		$ (33)	(95,830)			(95,863)
Share-based Compensation, Shares			208,238
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures			$ 1
Share-based Compensation, Value	3,186			2,633			2,634	552
Distributions on Common Shares and Units	(53,042)					(52,862)	(52,862)	(180)
Distributions on Preferred Shares	(8,063)					(8,047)	(8,047)	(16)
Net contribution from Non-controlling Interests	106							106
Unrealized gain (loss) on derivative instruments	811				811		811
Net income (loss)	$ 57,759					57,546	57,546	213
Preferred stock, shares outstanding at Jun. 30, 2017	10,000,000	10,000,000
Common stock, shares, outstanding at Jun. 30, 2017	68,816,375		68,816,375
Ending balance at Jun. 30, 2017	$ 1,514,451	$ 100	$ 688	$ 1,683,647	$ (1,501)	$ (172,590)	$ 1,510,344	$ 4,107