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	120,821	$ 50		120,771			120,821
Redemption of preferred shares, Shares		(9,000,000)
Redemption of preferred shares	(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	606			606			606
Repurchase of common shares, Shares			(88,510)
Repurchase of common shares	(2,496)		$ (1)	(2,495)			(2,496)
Share-based compensation, Shares			254,878
Share-based compensation			$ 3
Share-based compensation	6,185			5,354			5,357	828
Distributions on common shares/units	(83,146)					(82,877)	(82,877)	(269)
Distributions on preferred shares	(15,647)					(15,638)	(15,638)	(9)
Unrealized gain (loss) on derivative instruments	(13,112)				(13,112)		(13,112)
Net income (loss)	55,540					55,346	55,346	194
Preferred stock, shares outstanding at Sep. 30, 2016		10,000,000
Common stock, shares, outstanding at Sep. 30, 2016			71,922,904
Ending balance at Sep. 30, 2016	$ 1,604,535	$ 100	$ 719	1,774,413	(17,862)	(156,024)	1,601,346	3,189
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		$ 0	$ 0
Issuance of shares, net of offering 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	503		$ 1	502			503
Repurchase of common shares, Shares			(3,335,278)
Repurchase of common shares	(95,981)		$ (33)	(95,948)			(95,981)
Share-based compensation, Shares			208,238
Share-based compensation			$ 1
Share-based compensation	3,717			2,889			2,890	827
Distributions on common shares/units	(79,537)					(79,268)	(79,268)	(269)
Distributions on preferred shares	(12,085)					(12,070)	(12,070)	(15)
Net contribution from non-controlling interests	106							106
Unrealized gain (loss) on derivative instruments	1,544				1,544		1,544
Net income (loss)	$ 88,330					87,989	87,989	341
Preferred stock, shares outstanding at Sep. 30, 2017	10,000,000	10,000,000
Common stock, shares, outstanding at Sep. 30, 2017	68,812,575		68,812,575
Ending balance at Sep. 30, 2017	$ 1,515,651	$ 100	$ 688	$ 1,683,785	$ (768)	$ (172,576)	$ 1,511,229	$ 4,422