Consolidated Statement of Equity - 9 months ended Sep. 30, 2017 - USD ($) shares in Thousands, $ in Thousands	Total	Shares of Beneficial Interest at Par Value [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Parent [Member]	Noncontrolling Interest [Member]
Balance (in shares) at Dec. 31, 2016		74,606
Balance at Dec. 31, 2016	$ 1,052,062	$ 746	$ 1,368,636	$ (326,047)	$ 7,611	$ 1,050,946	$ 1,116
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to the controlling interests	17,331			17,331		17,331
Net loss attributable to the noncontrolling interests	(56)						(56)
Unrealized loss on interest rate hedge	(763)				(763)	(763)
Distributions to noncontrolling interests	(67)						(67)
Operating partnership units issued with acquisition	376						376
Dividends	(69,252)			(69,252)		(69,252)
Equity offerings, net of issuance costs (in shares)		3,587
Equity issuances, net of issuance costs	113,225	$ 36	113,189			113,225
Shares issued under dividend reinvestment program (in shares)		77
Shares issued under dividend reinvestment program	2,482	$ 1	2,481			2,482
Share grants, net of forfeitures (in shares)		194
Share grants, net of share grant amortization, forfeitures and tax withholdings	2,853	$ 2	2,851			2,853
Balance (in shares) at Sep. 30, 2017		78,464
Balance at Sep. 30, 2017	$ 1,118,191	$ 785	$ 1,487,157	$ (377,968)	$ 6,848	$ 1,116,822	$ 1,369