Consolidated Statements of Beneficiaries' Equity - USD ($) $ in Thousands	Total	Common Stock	Number of 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, 2018		176,873,324	977,120
Beginning balance at Dec. 31, 2018	$ 1,811,028	$ 1,770	$ 14,021	$ 3,200,312	$ (14,021)	$ 775,625	$ 5,029	$ (2,183,909)	$ 12,201
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	4,583					4,523			60
Other comprehensive income (loss)	$ (2,483)						(2,469)		(14)
Repurchase and retirement of Common Shares of Beneficial Interest (in shares)	(1,337,169)	(1,337,169)
Repurchase and retirement of Common Shares of Beneficial Interest	$ (17,281)	$ (13)		(17,268)
Share-based compensation activity (in shares)		465,883	41,342
Share-based compensation activity	3,677	$ 4		3,673
Share Issuance from/(to) Deferred Compensation Plan (in shares)		(458)	(5,920)
Share Issuance from/(to) Deferred Compensation Plan	0		$ 619		(619)
Reallocation of Noncontrolling interest	0			57					(57)
Issuance of partnership interest in consolidated real estate ventures	22								22
Distributions declared	(33,747)							(33,560)	(187)
Ending balance (in shares) at Mar. 31, 2019		176,001,580	1,012,542
Ending balance at Mar. 31, 2019	1,760,463	$ 1,761	$ 14,640	3,186,774	(14,640)	774,812	2,560	(2,217,469)	12,025
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