Consolidated Statements of Beneficiaries' Equity - USD ($)	Total	Common Stock [Member]	Deferred Compensation, Share-based Payments [Member]	Additional Paid-in Capital [Member]	Common Stock In Grantor Trust [Member]	Cumulative Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Cumulative Distributions [Member]	Noncontrolling Interest [Member]
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, Shares at Dec. 31, 2017		178,285,236	894,736
Net income	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, 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, Shares		68,425
Share Issuance from/(to) Deferred Compensation Plan	$ 0		$ 1,061,000		(1,061,000)
Share Issuance from/(to) Deferred Compensation Plan, Shares		66,830	53,856
Share Choice Plan issuance	0	(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, 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, Shares at Dec. 31, 2017		178,285,236	894,736
Net income	57,321,000
Other comprehensive income (loss)	6,879,000
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, Shares at Jun. 30, 2018		178,604,473	982,305
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, Shares at Mar. 31, 2018		178,442,517	948,592
Net income	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, 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, 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, Shares at Jun. 30, 2018		178,604,473	982,305
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, Shares at Dec. 31, 2018		176,873,324	977,120
Cumulative effect of accounting change	(5,336,000)					(5,336,000)
Net income	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, 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, Shares		465,883	41,342
Share Issuance from/(to) Deferred Compensation Plan	0		$ 619,000		(619,000)
Share Issuance from/(to) Deferred Compensation Plan, 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, 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, Shares at Dec. 31, 2018		176,873,324	977,120
Net income	10,835,000
Other comprehensive income (loss)	(7,229,000)
Repurchase and retirement of Common Shares of Beneficial Interest	$ (17,300,000)
Repurchase and retirement of Common Shares of Beneficial Interest, Shares	(1,337,169)
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, Shares at Jun. 30, 2019		176,197,883	1,113,450
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, Shares at Mar. 31, 2019		176,001,580	1,012,542
Net income	6,252,000					6,205,000			47,000
Other comprehensive income (loss)	(4,746,000)						(4,720,000)		(26,000)
Repurchase and retirement of Common Shares of Beneficial Interest	$ 0
Repurchase and retirement of Common Shares of Beneficial Interest, Shares	0
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, Shares		1,245
Share-based compensation activity	1,451,000	$ 2,000		1,449,000
Share-based compensation activity, Shares		94,150
Share Issuance from/(to) Deferred Compensation Plan	0		$ 1,599,000		(1,599,000)
Share Issuance from/(to) Deferred Compensation Plan, 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, Shares at Jun. 30, 2019		176,197,883	1,113,450