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]
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)	0
Unrealized gain (loss) on derivative instruments	(11,484)				(11,484)		(11,484)
Net income (loss)	16,637					16,579	16,579	58
Preferred stock, shares outstanding at Mar. 31, 2016		8,400,000
Common stock, shares, outstanding at Mar. 31, 2016			71,922,904
Ending balance at Mar. 31, 2016	$ 1,592,307	$ 84	$ 719	1,731,920	(16,234)	(126,871)	1,589,618	2,689
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	(62)	$ 0	$ 0	(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			(2,210,690)
Repurchase of Common Shares, Value	(62,444)		$ (22)	(62,422)			(62,444)
Share-based Compensation, Shares			208,238
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures			$ 1
Share-based Compensation, Value	1,127			850			851	276
Distributions on Common Shares and Units	(26,531)					(26,441)	(26,441)	(90)
Distributions on Preferred Shares	(4,023)					(4,023)	(4,023)	0
Net contribution from Non-controlling Interests	107							107
Unrealized gain (loss) on derivative instruments	2,104				2,104		2,104
Net income (loss)	$ 14,089					14,034	14,034	55
Preferred stock, shares outstanding at Mar. 31, 2017	10,000,000	10,000,000
Common stock, shares, outstanding at Mar. 31, 2017	69,937,163		69,937,163
Ending balance at Mar. 31, 2017	$ 1,533,986	$ 100	$ 699	$ 1,715,272	$ (208)	$ (185,657)	$ 1,530,206	$ 3,780