Consolidated Statements of Beneficiaries' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Deferred Compensation Payable in Common Shares	Additional Paid-in Capital	Common Shares in Grantor Trust	Cumulative Earnings	Cumulative Earnings Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income (Loss)	Cumulative Distributions	Noncontrolling Interests
Beginning balance (in shares) at Dec. 31, 2017			178,285,236	894,736
Beneficiaries' Equity, beginning balance at Dec. 31, 2017	$ 1,826,870		$ 1,784	$ 12,445	$ 3,218,077	$ (12,445)	$ 641,093		$ 2,399	$ (2,053,741)	$ 17,258
Net income	135,472						134,518				954
Other comprehensive income	2,669								2,630		39
Issuance of Common Shares of Beneficial Interest (in shares)			23,311
Issuance of Common Shares of Beneficial Interest	$ 416				416
Repurchase and retirement of Common Shares of Beneficial Interest (in shares)	(1,729,278)		(1,729,278)
Repurchase and retirement of Common Shares of Beneficial Interest	$ (21,858)		$ (17)		(21,841)
Issuance of partnership interest in consolidated real estate venture	16										16
Distributions from consolidated real estate venture	(94)										(94)
Share Choice Plan Issuance (in shares)			(1,285)
Redemption of LP Units	(7,043)										(7,043)
Share-based compensation activity (in shares)			196,151
Share-based compensation activity	5,845		$ 2		5,829		14
Share Issuance from/(to) Deferred Compensation Plan (in shares)			99,189	82,384
Share Issuance from/(to) Deferred Compensation Plan	(111)		$ 1	$ 1,576	(112)	(1,576)
Reallocation of Noncontrolling Interest	0				(2,057)						2,057
Distributions declared	(131,154)									(130,168)	(986)
Ending balance (in shares) at Dec. 31, 2018			176,873,324	977,120
Beneficiaries' Equity, ending balance at Dec. 31, 2018	1,811,028	$ (5,336)	$ 1,770	$ 14,021	3,200,312	(14,021)	775,625	$ (5,336)	5,029	(2,183,909)	12,201
Net income	34,529						34,267				262
Other comprehensive income	$ (7,440)								(7,399)		(41)
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)
Issuance of partnership interest in consolidated real estate venture	27										27
Purchase of partnership interest in consolidated real estate venture	(2,180)				(983)						(1,197)
Redemption of LP Units (in shares)			1,245
Redemption of LP Units	0				16						(16)
Share-based compensation activity (in shares)			845,210	41,342
Share-based compensation activity	10,027		$ 9		10,018
Share Issuance from/(to) Deferred Compensation Plan (in shares)			97,485	87,080
Share Issuance from/(to) Deferred Compensation Plan	0			$ 2,195		(2,195)
Reallocation of Noncontrolling Interest	0				63						(63)
Distributions declared	(135,071)									(134,324)	(747)
Ending balance (in shares) at Dec. 31, 2019			176,480,095	1,105,542
Beneficiaries' Equity, ending 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
Net income	307,326						305,527				1,799
Other comprehensive income	$ (5,220)								(5,191)		(29)
Repurchase and retirement of Common Shares of Beneficial Interest (in shares)	(6,248,483)		(6,248,483)
Repurchase and retirement of Common Shares of Beneficial Interest	$ (59,999)		$ (62)		(59,937)
Sale of partnership interest to consolidated real estate venture	(1,017)
Distributions from consolidated real estate venture	(22)
Share-based compensation activity (in shares)			309,096	50,967
Share-based compensation activity	6,236		$ 3		6,233
Share Issuance from/(to) Deferred Compensation Plan (in shares)			32,256	3,985
Share Issuance from/(to) Deferred Compensation Plan	(206)			$ 1,300	(206)	(1,300)
Reallocation of Noncontrolling Interest	0				(96)						96
Distributions declared	(130,753)									(130,005)	(748)
Ending balance (in shares) at Dec. 31, 2020			170,572,964	1,160,494
Beneficiaries' Equity, ending 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