Consolidated Statements of Equity - USD ($) shares in Thousands, $ in Thousands	Total	Shares of Beneficial Interest	Additional Paid in Capital	Distributions in Excess of Net Income	Accumulated Other Comprehensive Income (Loss)	Total Shareholders’ Equity	Noncontrolling Interests in Subsidiaries
Beginning Balance (in shares) at Dec. 31, 2019		82,099
Beginning Balance at Dec. 31, 2019	$ 1,412,062	$ 821	$ 1,592,487	$ (183,405)	$ 1,823	$ 1,411,726	$ 336
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(4,643)			(4,643)		(4,643)
Unrealized gain (loss) on interest rate hedges	(34,582)				(34,582)	(34,582)
Amortization of swap settlements	0
Distributions to noncontrolling interests	(11)						(11)
Dividends	$ (74,387)			(74,387)		(74,387)
Equity issuances, net of issuance costs (in shares)	46	46
Equity issuances, net of issuance costs	$ 1,242	$ 1	1,241			1,242
Shares issued under Dividend Reinvestment Program (in shares)	64	64
Shares issued under Dividend Reinvestment Program	$ 1,581	$ 1	1,580			1,581
Share grants, net of forfeitures and tax withholdings (in shares)		142
Share grants, net of forfeitures and tax withholdings	5,853	$ 1	5,852			5,853
Ending Balance (in shares) at Sep. 30, 2020		82,351
Ending Balance at Sep. 30, 2020	1,307,115	$ 824	1,601,160	(262,435)	(32,759)	1,306,790	325
Beginning Balance (in shares) at Jun. 30, 2020		82,327
Beginning Balance at Jun. 30, 2020	1,328,566	$ 823	1,598,620	(236,673)	(34,533)	1,328,237	329
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(956)			(956)		(956)
Unrealized gain (loss) on interest rate hedges	1,774				1,774	1,774
Amortization of swap settlements	0
Distributions to noncontrolling interests	(4)						(4)
Dividends	$ (24,806)			(24,806)		(24,806)
Shares issued under Dividend Reinvestment Program (in shares)	23	23
Shares issued under Dividend Reinvestment Program	$ 516	$ 1	515			516
Share grants, net of forfeitures and tax withholdings (in shares)		1
Share grants, net of forfeitures and tax withholdings	2,025		2,025			2,025
Ending Balance (in shares) at Sep. 30, 2020		82,351
Ending Balance at Sep. 30, 2020	1,307,115	$ 824	1,601,160	(262,435)	(32,759)	1,306,790	325
Beginning Balance (in shares) at Dec. 31, 2020		84,409
Beginning Balance at Dec. 31, 2020	1,321,109	$ 844	1,649,366	(298,860)	(30,563)	1,320,787	322
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	23,180			23,180		23,180
Unrealized gain (loss) on interest rate hedges	2,805				2,805	2,805
Loss on interest rate derivatives	5,760				5,760	5,760
Amortization of swap settlements	1,530				1,530	1,530
Distributions to noncontrolling interests	(13)						(13)
Dividends	$ (65,372)			(65,372)		(65,372)
Equity issuances, net of issuance costs (in shares)	24	24
Equity issuances, net of issuance costs	$ 467		467			467
Shares issued under Dividend Reinvestment Program (in shares)	65	65
Shares issued under Dividend Reinvestment Program	$ 1,468		1,468			1,468
Share grants, net of forfeitures and tax withholdings (in shares)		130
Share grants, net of forfeitures and tax withholdings	5,522	$ 2	5,520			5,522
Ending Balance (in shares) at Sep. 30, 2021		84,628
Ending Balance at Sep. 30, 2021	1,296,456	$ 846	1,656,821	(341,052)	(20,468)	1,296,147	309
Beginning Balance (in shares) at Jun. 30, 2021		84,590
Beginning Balance at Jun. 30, 2021	1,276,435	$ 846	1,654,409	(357,934)	(21,200)	1,276,121	314
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	31,319			31,319		31,319
Unrealized gain (loss) on interest rate hedges	221				221	221
Amortization of swap settlements	511				511	511
Distributions to noncontrolling interests	(5)						(5)
Dividends	$ (14,437)			(14,437)		(14,437)
Shares issued under Dividend Reinvestment Program (in shares)	19	20
Shares issued under Dividend Reinvestment Program	$ 459		459			459
Share grants, net of forfeitures and tax withholdings (in shares)		18
Share grants, net of forfeitures and tax withholdings	1,953		1,953			1,953
Ending Balance (in shares) at Sep. 30, 2021		84,628
Ending Balance at Sep. 30, 2021	$ 1,296,456	$ 846	$ 1,656,821	$ (341,052)	$ (20,468)	$ 1,296,147	$ 309