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 (loss)	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)
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, 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 (loss)	288,240
Other comprehensive income (loss)	$ (6,415)
Repurchase and retirement of Common Shares of Beneficial Interest (in shares)	(6,248,483)
Repurchase and retirement of Common Shares of Beneficial Interest	$ (60,000)
Ending balance (in shares) at Sep. 30, 2020		170,572,964	1,160,494
Ending balance at Sep. 30, 2020	1,815,782	$ 1,707	$ 17,516	3,136,851	(17,516)	1,091,095	(8,749)	(2,415,736)	10,614
Beginning balance (in shares) at Mar. 31, 2020		170,965,987	1,117,783
Beginning 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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	4,020					3,996			24
Other comprehensive income (loss)	226						225		1
Repurchase and retirement of Common Shares of Beneficial Interest (in shares)		(604,283)
Repurchase and retirement of Common Shares of Beneficial Interest	(6,141)	$ (5)		(6,136)
Share-based compensation activity (in shares)		166,628
Share-based compensation activity	1,668	$ 2		1,666
Share Issuance from/(to) Deferred Compensation Plan (in shares)		44,827	42,906
Share Issuance from/(to) Deferred Compensation Plan	(11)		$ 504	(11)	(504)
Reallocation of Noncontrolling interest	0			(123)					123
Distributions declared	(32,727)							(32,540)	(187)
Ending balance (in shares) at Jun. 30, 2020		170,573,159	1,160,689
Ending balance at Jun. 30, 2020	1,570,849	$ 1,707	$ 17,516	3,135,590	(17,516)	816,574	(9,970)	(2,383,273)	10,221
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	276,133					274,521			1,612
Other comprehensive income (loss)	1,228						1,221		7
Impact of deconsolidation of real estate venture	(1,017)								(1,017)
Distributions from consolidated real estate ventures	(22)								(22)
Share-based compensation activity	1,263			1,263
Share Issuance from/(to) Deferred Compensation Plan (in shares)		(195)	(195)
Share Issuance from/(to) Deferred Compensation Plan	(2)			(2)
Distributions declared	(32,650)							(32,463)	(187)
Ending balance (in shares) at Sep. 30, 2020		170,572,964	1,160,494
Ending balance at Sep. 30, 2020	1,815,782	$ 1,707	$ 17,516	3,136,851	(17,516)	1,091,095	(8,749)	(2,415,736)	10,614
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 (loss)	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
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 (loss)	7,763
Other comprehensive income (loss)	$ 3,245
Repurchase and retirement of Common Shares of Beneficial Interest (in shares)	0
Ending balance (in shares) at Sep. 30, 2021		171,126,257	1,169,703
Ending balance at Sep. 30, 2021	$ 1,725,477	$ 1,712	$ 18,491	3,145,209	(18,491)	1,117,804	(4,333)	(2,545,979)	11,064
Beginning balance (in shares) at Mar. 31, 2021		170,663,251	1,111,777
Beginning 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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(175)					(167)			(8)
Other comprehensive income (loss)	1,048						1,042		6
Issuance of partnership interest in consolidated real estate ventures	2,289								2,289
Redemption of LP Units	(2,334)								(2,334)
Share-based compensation activity (in shares)		237,240	63,566
Share-based compensation activity	690	$ 2		688
Share Issuance from/(to) Deferred Compensation Plan	0		$ 833		(833)
Reallocation of Noncontrolling interest	0			(569)					569
Distributions declared	(32,719)							(32,562)	(157)
Ending balance (in shares) at Jun. 30, 2021		170,900,491	1,175,343
Ending balance at Jun. 30, 2021	1,751,053	$ 1,709	$ 18,491	3,140,575	(18,491)	1,116,837	(5,427)	(2,513,373)	10,732
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	974					967			7
Other comprehensive income (loss)	1,099						1,094		5
Issuance of Common Shares of Beneficial Interest (in shares)		226,695
Issuance of Common Shares of Beneficial Interest	3,052	$ 3		3,049
Issuance of partnership interest in consolidated real estate ventures	476								476
Share-based compensation activity (in shares)		(929)	(5,640)
Share-based compensation activity	1,585			1,585
Distributions declared	(32,762)							(32,606)	(156)
Ending balance (in shares) at Sep. 30, 2021		171,126,257	1,169,703
Ending balance at Sep. 30, 2021	$ 1,725,477	$ 1,712	$ 18,491	$ 3,145,209	$ (18,491)	$ 1,117,804	$ (4,333)	$ (2,545,979)	$ 11,064