Consolidated Statements of Beneficiaries' Equity - USD ($)	Total	Common Stock	Deferred Compensation Payable in Common Shares	Additional Paid-in Capital	Common Shares in Grantor Trust	Cumulative Earnings	Accumulated Other Comprehensive Income (Loss)	Cumulative Distributions	Noncontrolling Interests
Beginning balance at Dec. 31, 2017	$ 1,826,870,000	$ 1,784,000	$ 12,445,000	$ 3,218,077,000	$ (12,445,000)	$ 641,093,000	$ 2,399,000	$ (2,053,741,000)	$ 17,258,000
Beginning balance (in shares) at Dec. 31, 2017		178,285,236	894,736
Net income (loss)	44,445,000					44,070,000			375,000
Other comprehensive income (loss)	5,008,000						4,966,000		42,000
Issuance of Common Shares of Beneficial Interest	416,000			416,000
Issuance of Common Shares of Beneficial Interest (in shares)		23,311
Issuance of partnership interest in consolidated real estate ventures	15,000								15,000
Distributions from consolidated real estate ventures	(54,000)								(54,000)
Share-based compensation activity	3,076,000	$ 1,000		3,072,000		3,000
Share-based compensation activity (in shares)		68,425
Share Issuance from/(to) Deferred Compensation Plan	0		$ 1,061,000		(1,061,000)
Share Issuance from/(to) Deferred Compensation Plan (in shares)		66,830	53,856
Share Choice Plan issuance (in shares)		(1,285)
Reallocation of Noncontrolling interest	0			(5,000)					5,000
Distributions declared	(32,525,000)							(32,259,000)	(266,000)
Ending balance at Mar. 31, 2018	1,847,251,000	$ 1,785,000	$ 13,506,000	3,221,560,000	(13,506,000)	685,166,000	7,365,000	(2,086,000,000)	17,375,000
Ending balance (in shares) at Mar. 31, 2018		178,442,517	948,592
Beginning balance at Dec. 31, 2017	1,826,870,000	$ 1,784,000	$ 12,445,000	3,218,077,000	(12,445,000)	641,093,000	2,399,000	(2,053,741,000)	17,258,000
Beginning balance (in shares) at Dec. 31, 2017		178,285,236	894,736
Net income (loss)	13,799,000
Other comprehensive income (loss)	7,906,000
Ending balance at Sep. 30, 2018	1,756,294,000	$ 1,787,000	$ 14,021,000	3,223,318,000	(14,021,000)	654,744,000	10,239,000	(2,150,463,000)	16,669,000
Ending balance (in shares) at Sep. 30, 2018		178,602,602	977,120
Beginning balance at Mar. 31, 2018	1,847,251,000	$ 1,785,000	$ 13,506,000	3,221,560,000	(13,506,000)	685,166,000	7,365,000	(2,086,000,000)	17,375,000
Beginning balance (in shares) at Mar. 31, 2018		178,442,517	948,592
Net income (loss)	12,876,000					12,747,000			129,000
Other comprehensive income (loss)	1,871,000						1,856,000		15,000
Issuance of partnership interest in consolidated real estate ventures	(4,000)								(4,000)
Share-based compensation activity	1,139,000	$ 1,000		1,135,000		3,000
Share-based compensation activity (in shares)		127,726
Share Issuance from/(to) Deferred Compensation Plan	(111,000)	$ 1,000	$ 530,000	(112,000)	(530,000)
Share Issuance from/(to) Deferred Compensation Plan (in shares)		34,230	33,713
Reallocation of Noncontrolling interest	0			2,000					(2,000)
Distributions declared	(32,497,000)							(32,230,000)	(267,000)
Ending balance at Jun. 30, 2018	1,830,525,000	$ 1,787,000	$ 14,036,000	3,222,585,000	(14,036,000)	697,916,000	9,221,000	(2,118,230,000)	17,246,000
Ending balance (in shares) at Jun. 30, 2018		178,604,473	982,305
Net income (loss)	(43,522,000)					(43,180,000)			(342,000)
Other comprehensive income (loss)	1,027,000						1,018,000		9,000
Issuance of partnership interest in consolidated real estate ventures	5,000								5,000
Share-based compensation activity	758,000			750,000		8,000
Share Issuance from/(to) Deferred Compensation Plan	0		$ (15,000)		15,000
Share Issuance from/(to) Deferred Compensation Plan (in shares)		(1,871)	(5,185)
Reallocation of Noncontrolling interest	0			(17,000)					17,000
Distributions declared	(32,499,000)							(32,233,000)	(266,000)
Ending balance at Sep. 30, 2018	1,756,294,000	$ 1,787,000	$ 14,021,000	3,223,318,000	(14,021,000)	654,744,000	10,239,000	(2,150,463,000)	16,669,000
Ending balance (in shares) at Sep. 30, 2018		178,602,602	977,120
Beginning balance at Dec. 31, 2018	1,811,028,000	$ 1,770,000	$ 14,021,000	3,200,312,000	(14,021,000)	775,625,000	5,029,000	(2,183,909,000)	12,201,000
Beginning balance (in shares) at Dec. 31, 2018		176,873,324	977,120
Net income (loss)	4,583,000					4,523,000			60,000
Other comprehensive income (loss)	(2,483,000)						(2,469,000)		(14,000)
Repurchase and retirement of Common Shares of Beneficial Interest	(17,281,000)	$ (13,000)		(17,268,000)
Repurchase and retirement of Common Shares of Beneficial Interest (in shares)		(1,337,169)
Issuance of partnership interest in consolidated real estate ventures	22,000								22,000
Share-based compensation activity	3,677,000	$ 4,000		3,673,000
Share-based compensation activity (in shares)		465,883	41,342
Share Issuance from/(to) Deferred Compensation Plan	0		$ 619,000		(619,000)
Share Issuance from/(to) Deferred Compensation Plan (in shares)		(458)	(5,920)
Reallocation of Noncontrolling interest	0			57,000					(57,000)
Distributions declared	(33,747,000)							(33,560,000)	(187,000)
Ending balance at Mar. 31, 2019	1,760,463,000	$ 1,761,000	$ 14,640,000	3,186,774,000	(14,640,000)	774,812,000	2,560,000	(2,217,469,000)	12,025,000
Ending balance (in shares) at Mar. 31, 2019		176,001,580	1,012,542
Beginning balance at Dec. 31, 2018	1,811,028,000	$ 1,770,000	$ 14,021,000	3,200,312,000	(14,021,000)	775,625,000	5,029,000	(2,183,909,000)	12,201,000
Beginning balance (in shares) at Dec. 31, 2018		176,873,324	977,120
Net income (loss)	17,655,000
Other comprehensive income (loss)	(8,627,000)
Repurchase and retirement of Common Shares of Beneficial Interest	$ (17,300,000)
Repurchase and retirement of Common Shares of Beneficial Interest (in shares)	(1,337,169)
Ending balance at Sep. 30, 2019	$ 1,702,437,000	$ 1,763,000	$ 16,216,000	3,189,350,000	(16,216,000)	787,789,000	(3,550,000)	(2,284,610,000)	11,695,000
Ending balance (in shares) at Sep. 30, 2019		176,194,918	1,105,542
Beginning balance at Mar. 31, 2019	1,760,463,000	$ 1,761,000	$ 14,640,000	3,186,774,000	(14,640,000)	774,812,000	2,560,000	(2,217,469,000)	12,025,000
Beginning balance (in shares) at Mar. 31, 2019		176,001,580	1,012,542
Net income (loss)	6,252,000					6,205,000			47,000
Other comprehensive income (loss)	(4,746,000)						(4,720,000)		(26,000)
Issuance of partnership interest in consolidated real estate ventures	3,000								3,000
Redemption of LP Units	0			16,000					(16,000)
Redemption of LP Units (in shares)		1,245
Share-based compensation activity	1,451,000	$ 2,000		1,449,000
Share-based compensation activity (in shares)		94,150
Share Issuance from/(to) Deferred Compensation Plan	0		$ 1,599,000		(1,599,000)
Share Issuance from/(to) Deferred Compensation Plan (in shares)		100,908	100,908
Distributions declared	(33,758,000)							(33,571,000)	(187,000)
Ending balance at Jun. 30, 2019	1,729,665,000	$ 1,763,000	$ 16,239,000	3,188,239,000	(16,239,000)	781,017,000	(2,160,000)	(2,251,040,000)	11,846,000
Ending balance (in shares) at Jun. 30, 2019		176,197,883	1,113,450
Net income (loss)	6,820,000					6,772,000			48,000
Other comprehensive income (loss)	(1,398,000)						(1,390,000)		(8,000)
Repurchase and retirement of Common Shares of Beneficial Interest	0
Issuance of partnership interest in consolidated real estate ventures	2,000								2,000
Share-based compensation activity	1,105,000			1,105,000
Share Issuance from/(to) Deferred Compensation Plan	0		$ (23,000)		23,000
Share Issuance from/(to) Deferred Compensation Plan (in shares)		(2,965)	(7,908)
Reallocation of Noncontrolling interest	0			6,000					(6,000)
Distributions declared	(33,757,000)							(33,570,000)	(187,000)
Ending balance at Sep. 30, 2019	$ 1,702,437,000	$ 1,763,000	$ 16,216,000	$ 3,189,350,000	$ (16,216,000)	$ 787,789,000	$ (3,550,000)	$ (2,284,610,000)	$ 11,695,000
Ending balance (in shares) at Sep. 30, 2019		176,194,918	1,105,542