CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (Unaudited) - USD ($) $ in Thousands	Total	PREFERRED SHARES	COMMON SHARES, $0.01 PAR VALUE	PAID IN CAPITAL	RETAINED EARNINGS	ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)	DISTRIBUTIONS	OPERATING PARTNERSHIP	PARTIALLY OWNED PROPERTIES
Balance, beginning of year at Dec. 31, 2018		$ 37,280	$ 3,694	$ 8,935,453	$ 1,261,763	$ (64,986)
Balance, beginning of year at Dec. 31, 2018								$ 228,738	$ (2,293)
COMMON SHARES, $0.01 PAR VALUE
Conversion of OP Units into Common Shares			3	9,840
Exercise of share options			14	67,052
Employee Share Purchase Plan (ESPP)				2,323
Share-based employee compensation expense:
Restricted shares			2	10,302
Share options				2,185
ESPP discount				502
Offering costs				(789)
Supplemental Executive Retirement Plan (SERP)				(1,539)
Change in market value of Redeemable Noncontrolling Interests –Operating Partnership	$ 114,936			(114,936)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				6,919				(6,919)
PAID IN CAPITAL
Conversion of OP Units into Common Shares			3	9,840
Exercise of share options			14	67,052
Employee Share Purchase Plan (ESPP)				2,323
RETAINED EARNINGS
Net income attributable to controlling interests	680,613				680,613
Common Share distributions					(631,635)
Preferred Share distributions					(2,318)
Accumulated other comprehensive income (loss) - derivative instruments:
Unrealized holding gains (losses) arising during the period	(33,765)					(33,765)
Losses reclassified into earnings from other comprehensive income	(14,659)					14,659
DISTRIBUTIONS
Distributions declared per Common Share outstanding							$ 1.7025
NONCONTROLLING INTERESTS
Conversion of OP Units held by Noncontrolling Interests into OP Units held by General Partner								(9,843)
Equity compensation associated with Noncontrolling Interests								12,200
Net income attributable to Noncontrolling Interests	25,339							25,339	2,450
Distributions to Noncontrolling Interests								(22,493)	(6,453)
Change in carrying value of Redeemable Noncontrolling Interests - Operating Partnership	957							(957)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				6,919				(6,919)
PARTIALLY OWNED PROPERTIES
Net income attributable to Noncontrolling Interests	25,339							25,339	2,450
Contributions by Noncontrolling Interests									4,594
Distributions to Noncontrolling Interests								(22,493)	(6,453)
Balance, end of period at Sep. 30, 2019		37,280	3,713	8,917,312	1,308,423	(84,092)
Balance, end of period at Sep. 30, 2019								226,065	(1,702)
Balance, beginning of year at Jun. 30, 2019		37,280	3,708	8,949,581	1,252,809	(89,849)
Balance, beginning of year at Jun. 30, 2019								227,320	(1,298)
COMMON SHARES, $0.01 PAR VALUE
Conversion of OP Units into Common Shares			1	4,971
Exercise of share options			4	18,575
Employee Share Purchase Plan (ESPP)				671
Share-based employee compensation expense:
Restricted shares				2,322
Share options				503
ESPP discount				137
Offering costs				(634)
Change in market value of Redeemable Noncontrolling Interests –Operating Partnership				(57,962)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				(852)				852
PAID IN CAPITAL
Conversion of OP Units into Common Shares			1	4,971
Exercise of share options			4	18,575
Employee Share Purchase Plan (ESPP)				671
RETAINED EARNINGS
Net income attributable to controlling interests	267,106				267,106
Common Share distributions					(210,719)
Preferred Share distributions					(773)
Accumulated other comprehensive income (loss) - derivative instruments:
Losses reclassified into earnings from other comprehensive income	(5,757)					5,757
DISTRIBUTIONS
Distributions declared per Common Share outstanding							0.5675
NONCONTROLLING INTERESTS
Conversion of OP Units held by Noncontrolling Interests into OP Units held by General Partner								(4,972)
Equity compensation associated with Noncontrolling Interests								1,371
Net income attributable to Noncontrolling Interests	9,910							9,910	830
Distributions to Noncontrolling Interests								(7,414)	(1,234)
Change in carrying value of Redeemable Noncontrolling Interests - Operating Partnership								(1,002)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				(852)				852
PARTIALLY OWNED PROPERTIES
Net income attributable to Noncontrolling Interests	9,910							9,910	830
Distributions to Noncontrolling Interests								(7,414)	(1,234)
Balance, end of period at Sep. 30, 2019		37,280	3,713	8,917,312	1,308,423	(84,092)
Balance, end of period at Sep. 30, 2019								226,065	(1,702)
Balance, beginning of year at Dec. 31, 2019	10,315,506	37,280	3,717	8,965,577	1,386,495	(77,563)
Balance, beginning of year at Dec. 31, 2019	229,020							227,837	1,183
COMMON SHARES, $0.01 PAR VALUE
Conversion of OP Units into Common Shares			1	3,912
Exercise of share options			2	11,424
Employee Share Purchase Plan (ESPP)				3,556
Share-based employee compensation expense:
Restricted shares			2	9,236
Share options				1,819
ESPP discount				626
Supplemental Executive Retirement Plan (SERP)				(395)
Change in market value of Redeemable Noncontrolling Interests –Operating Partnership	(169,825)			169,825
Adjustment for Noncontrolling Interests ownership in Operating Partnership				438				(438)
PAID IN CAPITAL
Conversion of OP Units into Common Shares			1	3,912
Exercise of share options			2	11,424
Employee Share Purchase Plan (ESPP)				3,556
RETAINED EARNINGS
Net income attributable to controlling interests	660,780				660,780
Common Share distributions					(673,019)
Preferred Share distributions					(2,318)
Accumulated other comprehensive income (loss) - derivative instruments:
Unrealized holding gains (losses) arising during the period	(1,190)					(1,190)
Losses reclassified into earnings from other comprehensive income	(17,275)					17,275
DISTRIBUTIONS
Distributions declared per Common Share outstanding							1.8075
NONCONTROLLING INTERESTS
Issuance of restricted units to Noncontrolling Interests								12
Conversion of OP Units held by Noncontrolling Interests into OP Units held by General Partner								(3,913)
Equity compensation associated with Noncontrolling Interests								9,525
Net income attributable to Noncontrolling Interests	24,624							24,624	14,113
Distributions to Noncontrolling Interests								(25,000)	(11,343)
Change in carrying value of Redeemable Noncontrolling Interests - Operating Partnership	131							(131)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				438				(438)
PARTIALLY OWNED PROPERTIES
Net income attributable to Noncontrolling Interests	24,624							24,624	14,113
Contributions by Noncontrolling Interests									417
Distributions to Noncontrolling Interests								(25,000)	(11,343)
Balance, end of period at Sep. 30, 2020	10,517,480	37,280	3,722	9,166,018	1,371,938	(61,478)
Balance, end of period at Sep. 30, 2020	236,886							232,516	4,370
Balance, beginning of year at Jun. 30, 2020		37,280	3,722	9,118,332	1,505,694	(67,355)
Balance, beginning of year at Jun. 30, 2020								235,169	4,634
COMMON SHARES, $0.01 PAR VALUE
Conversion of OP Units into Common Shares				57
Exercise of share options				104
Employee Share Purchase Plan (ESPP)				1,197
Share-based employee compensation expense:
Restricted shares				1,984
Share options				526
ESPP discount				210
Supplemental Executive Retirement Plan (SERP)				111
Change in market value of Redeemable Noncontrolling Interests –Operating Partnership				41,072
Adjustment for Noncontrolling Interests ownership in Operating Partnership				2,425				(2,425)
PAID IN CAPITAL
Conversion of OP Units into Common Shares				57
Exercise of share options				104
Employee Share Purchase Plan (ESPP)				1,197
RETAINED EARNINGS
Net income attributable to controlling interests	91,286				91,286
Common Share distributions					(224,269)
Preferred Share distributions					(773)
Accumulated other comprehensive income (loss) - derivative instruments:
Losses reclassified into earnings from other comprehensive income	(5,877)					5,877
DISTRIBUTIONS
Distributions declared per Common Share outstanding							$ 0.6025
NONCONTROLLING INTERESTS
Conversion of OP Units held by Noncontrolling Interests into OP Units held by General Partner								(57)
Equity compensation associated with Noncontrolling Interests								2,499
Net income attributable to Noncontrolling Interests	3,376							3,376	703
Distributions to Noncontrolling Interests								(7,963)	(1,043)
Change in carrying value of Redeemable Noncontrolling Interests - Operating Partnership								1,917
Adjustment for Noncontrolling Interests ownership in Operating Partnership				2,425				(2,425)
PARTIALLY OWNED PROPERTIES
Net income attributable to Noncontrolling Interests	3,376							3,376	703
Contributions by Noncontrolling Interests									76
Distributions to Noncontrolling Interests								(7,963)	(1,043)
Balance, end of period at Sep. 30, 2020	10,517,480	$ 37,280	$ 3,722	$ 9,166,018	$ 1,371,938	$ (61,478)
Balance, end of period at Sep. 30, 2020	$ 236,886							$ 232,516	$ 4,370