Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Preferred Shares	Common Shares	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Distributions in Excess of Retained Earnings	Total Shareholders' Equity	Non-Controlling Interests
Preferred stock, beginning balance (in shares) at Dec. 31, 2015		14,000,000
Common stock, beginning balance (in shares) 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 (in shares)		5,000,000
Issuance of shares, net of offering costs	120,808	$ 50		120,758			120,808
Redemption of preferred shares (in 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 (in shares)			21,407
Issuance of common shares for Board of Trustee compensation	606			606			606
Repurchase of common shares (in shares)			(88,510)
Repurchase of common shares	(2,496)		$ (1)	(2,495)			(2,496)
Share-based compensation (in shares)			254,878
Share-based compensation	8,466		$ 3	7,358			7,361	1,105
Distributions on common shares/units	(110,773)					(110,414)	(110,414)	(359)
Distributions on preferred shares	(19,679)					(19,662)	(19,662)	(17)
Other comprehensive income (loss):
Unrealized gain (loss) on derivative instruments	2,438				2,438		2,438
Net income (loss)	73,962					73,704	73,704	258
Preferred stock, ending balance (in shares) at Dec. 31, 2016		10,000,000
Common stock, ending balance (in shares) at Dec. 31, 2016			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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Offering costs	(62)			(62)			(62)
Issuance of common shares for Board of Trustees compensation (in shares)			16,711
Issuance of common shares for Board of Trustee compensation	503		$ 1	502			503
Repurchase of common shares (in shares)			(3,335,278)
Repurchase of common shares	(95,981)		$ (33)	(95,948)			(95,981)
Share-based compensation (in shares)			208,238
Share-based compensation	5,646		$ 1	4,541			4,542	1,104
Distributions on common shares/units	(105,939)					(105,580)	(105,580)	(359)
Distributions on preferred shares	(16,126)					(16,094)	(16,094)	(32)
Redemption of non-controlling interest LTIP units	106							106
Other comprehensive income (loss):
Unrealized gain (loss) on derivative instruments	6,001				6,001		6,001
Net income (loss)	$ 100,262					99,888	99,888	374
Preferred stock, ending balance (in shares) at Dec. 31, 2017	10,000,000	10,000,000
Common stock, ending balance (in shares) at Dec. 31, 2017	68,812,575		68,812,575
Ending balance at Dec. 31, 2017	$ 1,503,526	$ 100	$ 688	1,685,437	3,689	(191,013)	1,498,901	4,625
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares, net of offering costs (in shares)		10,400,000	61,399,104
Issuance of shares, net of offering costs	2,377,807	$ 104	$ 614	2,377,089			2,377,807
Issuance of operating partnership units	4,665							4,665
Issuance of common shares for Board of Trustees compensation (in shares)			17,410
Issuance of common shares for Board of Trustee compensation	662		$ 1	661			662
Repurchase of common shares (in shares)			(69,687)
Repurchase of common shares	(2,507)		$ (1)	(2,506)			(2,507)
Share-based compensation (in shares)			151,887
Share-based compensation	6,228		$ 1	5,123			5,124	1,104
Distributions on common shares/units	(113,549)					(113,172)	(113,172)	(377)
Distributions on preferred shares	(17,505)					(17,466)	(17,466)	(39)
Net contribution from non-controlling interests	125							125
Other comprehensive income (loss):
Unrealized gain (loss) on derivative instruments	(2,907)				(2,907)		(2,907)
Net income (loss)	$ 13,385					13,393	13,393	(8)
Preferred stock, ending balance (in shares) at Dec. 31, 2018	20,400,000	20,400,000
Common stock, ending balance (in shares) at Dec. 31, 2018	130,311,289		130,311,289
Ending balance at Dec. 31, 2018	$ 3,769,930	$ 204	$ 1,303	$ 4,065,804	$ 1,330	$ (308,806)	$ 3,759,835	$ 10,095