Consolidated Statement of Changes In Equity - USD ($) $ in Thousands	Total	Common Stock	Paid-in Capital	Redeemable Perpetual Preferred Stock	Distributions in Excess of Accumulated Earnings	Accumulated Other Comprehensive Loss/(Income)	Non- controlling interests – Common OP Units
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of change in accounting principle	$ (15,186)				$ (15,186)
Adjusted balance	1,084,856	$ 883	$ 1,242,109	$ 0	(227,166)	$ 942	$ 68,088
Balance at Dec. 31, 2017	1,100,042	883	1,242,109	0	(211,980)	942	68,088
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exchange of Common OP Units for Common Stock		1	161				(162)
Issuance of Common Stock through employee stock purchase plan	846		846
Compensation expenses related to restricted stock and stock options	4,541		4,541
Adjustment for Common OP Unitholders in the Operating Partnership	0		725				(725)
Adjustment for fair market value of swap	2,637					2,637
Consolidated net income	113,346			8	106,359		6,979
Distributions	(104,060)			(8)	(97,646)		(6,406)
Other	(335)		(335)
Balance at Jun. 30, 2018	$ 1,101,831	$ 884	$ 1,248,047	$ 0	$ (218,453)	$ 3,579	$ 67,774