Consolidated Statements of Changes In Equity - USD ($) $ in Thousands	Total	Common Stock	Paid-in Capital	Distributions in Excess of Accumulated Earnings	Accumulated Other Comprehensive Income (Loss)	Non- controlling interests – Common OP Units
Balance at Dec. 31, 2017	$ 1,100,042	$ 883	$ 1,242,109	$ (211,980)	$ 942	$ 68,088
Increase (Decrease) in Stockholders' Equity
Exchange of Common OP Units for common stock	0	0	80			(80)
Issuance of common stock through employee stock purchase plan	503		503
Compensation expenses related to restricted stock and stock options	1,800		1,800
Adjustment for Common OP Unitholders in the Operating Partnership	0		782			(782)
Adjustment for fair market value of swap	1,873				1,873
Consolidated net income	64,177			60,222		3,955
Distributions	(52,010)			(48,805)		(3,205)
Other	(60)		(60)	0
Balance at Mar. 31, 2018	1,101,139	883	1,245,214	(215,749)	2,815	67,976
Balance at Dec. 31, 2018	1,193,344	896	1,329,391	(211,034)	2,299	71,792
Increase (Decrease) in Stockholders' Equity
Exchange of Common OP Units for common stock	0		66			(66)
Issuance of common stock through exercise of options	53		53
Issuance of common stock through employee stock purchase plan	652		652
Compensation expenses related to restricted stock and stock options	2,420		2,420
Repurchase of common stock or Common OP Units	(53)		(53)
Adjustment for Common OP Unitholders in the Operating Partnership	0		(56)			56
Adjustment for fair market value of swap	(931)				(931)
Consolidated net income	120,535			113,309		7,226
Distributions	(58,639)			(55,123)		(3,516)
Other	(63)		(63)
Balance at Mar. 31, 2019	$ 1,257,318	$ 896	$ 1,332,410	$ (152,848)	$ 1,368	$ 75,492