Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Shares of Beneficial Interest at Par Value	Additional Paid in Capital	Distributions in Excess of Net Income	Accumulated Other Comprehensive Income	Total Shareholders’ Equity	Noncontrolling Interests in Subsidiaries
Balance (in shares) at Dec. 31, 2017		78,510,000
Balance at Dec. 31, 2017	$ 1,095,336	$ 785	$ 1,483,980	$ (399,213)	$ 9,419	$ 1,094,971	$ 365
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to the controlling interests	3,299			3,299		3,299
Unrealized gain (loss) on interest rate hedges	4,065				4,065	4,065
Distributions to noncontrolling interests	(3)						(3)
Dividends	$ (23,719)			(23,719)		(23,719)
Shares issued under dividend reinvestment program (in shares)	37,079	37,000
Shares issued under dividend reinvestment program	$ 717	$ 0	717			717
Share grants, net of forfeitures and tax withholdings (in shares)		89,000
Share grants, net of forfeitures and tax withholdings	1,069	$ 1	1,068			1,069
Balance (in shares) at Mar. 31, 2018		78,636,000
Balance at Mar. 31, 2018	1,080,764	$ 786	1,485,765	(419,633)	13,484	1,080,402	362
Balance (in shares) at Dec. 31, 2018		79,910,000
Balance at Dec. 31, 2018	1,068,478	$ 799	1,526,574	(469,085)	9,839	1,068,127	351
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to the controlling interests	(4,405)			(4,405)		(4,405)
Unrealized gain (loss) on interest rate hedges	(4,169)				(4,169)	(4,169)
Distributions to noncontrolling interests	(4)						(4)
Dividends	$ (24,141)			(24,141)		(24,141)
Shares issued under dividend reinvestment program (in shares)	42,842	43,000
Shares issued under dividend reinvestment program	$ 1,097	$ 0	1,097			1,097
Share grants, net of forfeitures and tax withholdings (in shares)		76,000
Share grants, net of forfeitures and tax withholdings	2,246	$ 1	2,245			2,246
Balance (in shares) at Mar. 31, 2019		80,029,000
Balance at Mar. 31, 2019	$ 1,038,196	$ 800	$ 1,529,916	$ (498,537)	$ 5,670	$ 1,037,849	$ 347