Consolidated Statements of Beneficiaries' Equity - USD ($) $ in Thousands	Total	Common Stock	Rabbi Trust/Deferred Compensation Shares	Additional Paid-in Capital	Common Shares in Grantor Trust	Cumulative Earnings	Accumulated Other Comprehensive Income (Loss)	Cumulative Distributions	Noncontrolling Interests
Beginning balance (in shares) at Dec. 31, 2019		176,480,095	1,105,542
Beginning balance at Dec. 31, 2019	$ 1,688,303	$ 1,766	$ 16,216	$ 3,192,158	$ (16,216)	$ 804,556	$ (2,370)	$ (2,318,233)	$ 10,426
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	8,087					8,022			65
Other comprehensive income (loss)	$ (7,869)						(7,825)		(44)
Repurchase and retirement of Common Shares of Beneficial Interest (in shares)	(5,644,200)	(5,644,200)
Repurchase and retirement of Common Shares of Beneficial Interest	$ (53,858)	$ (57)		(53,801)
Share-based compensation activity (in shares)		142,468	50,967
Share-based compensation activity	2,031	$ 1		2,030
Share Issuance from/(to) Deferred Compensation Plan (in shares)		(12,376)	(38,726)
Share Issuance from/(to) Deferred Compensation Plan	(193)		$ 796	(193)	(796)
Distributions declared	(32,687)							(32,500)	(187)
Ending balance (in shares) at Mar. 31, 2020		170,965,987	1,117,783
Ending balance at Mar. 31, 2020	1,603,814	$ 1,710	$ 17,012	3,140,194	(17,012)	812,578	(10,195)	(2,350,733)	10,260
Beginning balance (in shares) at Dec. 31, 2020		170,572,964	1,160,494
Beginning balance at Dec. 31, 2020	1,804,648	$ 1,707	$ 17,516	3,138,152	(17,516)	1,110,083	(7,561)	(2,448,238)	10,505
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	6,964					6,921			43
Other comprehensive income (loss)	1,098						1,092		6
Share-based compensation activity (in shares)		108,345	12,719
Share-based compensation activity	2,502			2,502
Share Issuance from/(to) Deferred Compensation Plan (in shares)		(18,058)	(61,436)
Share Issuance from/(to) Deferred Compensation Plan	(198)		$ 142	(198)	(142)
Distributions declared	(32,760)							(32,573)	(187)
Ending balance (in shares) at Mar. 31, 2021		170,663,251	1,111,777
Ending balance at Mar. 31, 2021	$ 1,782,254	$ 1,707	$ 17,658	$ 3,140,456	$ (17,658)	$ 1,117,004	$ (6,469)	$ (2,480,811)	$ 10,367