Consolidated Statements 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 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			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			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)
Balance at Mar. 31, 2018	1,101,139	883	1,245,214		(215,749)	2,815	67,976
Balance at Dec. 31, 2017	1,100,042	883	1,242,109		(211,980)	942	68,088
Increase (Decrease) in Stockholders' Equity
Adjustment for fair market value of swap	2,637
Balance at Jun. 30, 2018	1,101,831	884	1,248,047	$ 0	(218,453)	3,579	67,774
Balance at Mar. 31, 2018	1,101,139	883	1,245,214		(215,749)	2,815	67,976
Increase (Decrease) in Stockholders' Equity
Exchange of Common OP Units for common stock		1	81				(82)
Issuance of common stock through employee stock purchase plan	343		343
Compensation expenses related to restricted stock and stock options	2,741		2,741
Adjustment for Common OP Unitholders in the Operating Partnership			(57)				57
Adjustment for fair market value of swap	764					764
Consolidated net income	49,169			8	46,137		3,024
Distributions	(52,050)			(8)	(48,841)		(3,201)
Other	(275)		(275)
Balance at Jun. 30, 2018	1,101,831	884	1,248,047	0	(218,453)	3,579	67,774
Balance at Dec. 31, 2018	1,193,344	896	1,329,391	0	(211,034)	2,299	71,792
Increase (Decrease) in Stockholders' Equity
Exchange of Common OP Units for common stock			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			(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	0	(152,848)	1,368	75,492
Balance at Dec. 31, 2018	1,193,344	896	1,329,391	0	(211,034)	2,299	71,792
Increase (Decrease) in Stockholders' Equity
Adjustment for fair market value of swap	(2,541)
Balance at Jun. 30, 2019	1,307,474	906	1,397,613	0	(162,204)	(242)	71,401
Balance at Mar. 31, 2019	1,257,318	896	1,332,410	0	(152,848)	1,368	75,492
Increase (Decrease) in Stockholders' Equity
Exchange of Common OP Units for common stock		5	6,430				(6,435)
Issuance of common stock through employee stock purchase plan	587		587
Issuance of Common Stock	59,319	5	59,314
Compensation expenses related to restricted stock and stock options	2,625		2,625
Adjustment for Common OP Unitholders in the Operating Partnership			(2,883)				2,883
Adjustment for fair market value of swap	(1,610)					(1,610)	0
Consolidated net income	49,085			8	46,401		2,676
Distributions	(58,980)			(8)	(55,757)		(3,215)
Other	(870)		(870)
Balance at Jun. 30, 2019	$ 1,307,474	$ 906	$ 1,397,613	$ 0	$ (162,204)	$ (242)	$ 71,401