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, 2017		$ 37,280	$ 3,680	$ 8,886,586	$ 1,403,530	$ (88,612)
Balance, beginning of year at Dec. 31, 2017								$ 226,691	$ 4,708
COMMON SHARES, $0.01 PAR VALUE
Conversion of OP Units into Common Shares				356
Exercise of share options			2	5,998
Employee Share Purchase Plan (ESPP)			1	3,073
Share-based employee compensation expense:
Restricted shares			1	6,803
Share options				9,206
ESPP discount				604
Offering costs				(27)
Supplemental Executive Retirement Plan (SERP)				(533)
Change in market value of Redeemable Noncontrolling Interests – Operating Partnership	$ 14,361			(14,361)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				2,619				(2,619)
PAID IN CAPITAL
Conversion of OP Units into Common Shares				356
Exercise of share options			2	5,998
Employee Share Purchase Plan (ESPP)			1	3,073
RETAINED EARNINGS
Net income attributable to controlling interests	540,348				540,348
Common Share distributions					(596,735)
Preferred Share distributions					(2,318)
Accumulated other comprehensive income (loss) – derivative instruments:
Unrealized holding gains (losses) arising during the period	24,021					24,021
Losses reclassified into earnings from other comprehensive income	(13,902)					13,902
DISTRIBUTIONS
Distributions declared per Common Share outstanding							$ 1.62
NONCONTROLLING INTERESTS
Issuance of restricted units to Noncontrolling Interests								1
Conversion of OP Units into Common Shares				356
Equity compensation associated with Noncontrolling Interests								11,074
Net income	562,804
Distributions to Noncontrolling Interests								(21,560)	(8,930)
Change in carrying value of Redeemable Noncontrolling Interests - Operating Partnership	(77)							77
Adjustment for Noncontrolling Interests ownership in Operating Partnership				2,619				(2,619)
Conversion of OP Units held by Noncontrolling Interests into OP Units held by General Partner								(356)
Net income attributable to Noncontrolling Interests	20,517							20,517	1,939
PARTIALLY OWNED PROPERTIES
Net income attributable to Noncontrolling Interests	20,517							20,517	1,939
Contributions by Noncontrolling Interests									125
Distributions to Noncontrolling Interests								(21,560)	(8,930)
Balance, end of period at Sep. 30, 2018		37,280	3,684	8,900,324	1,344,825	(50,689)
Balance, end of period at Sep. 30, 2018								233,825	(2,158)
Balance, beginning of year at Jun. 30, 2018		37,280	3,683	8,905,184	1,329,600	(67,310)
Balance, beginning of year at Jun. 30, 2018								232,995	(1,646)
COMMON SHARES, $0.01 PAR VALUE
Conversion of OP Units into Common Shares				25
Exercise of share options			1	3,382
Employee Share Purchase Plan (ESPP)				893
Share-based employee compensation expense:
Restricted shares				1,641
Share options				670
ESPP discount				204
Supplemental Executive Retirement Plan (SERP)				5
Change in market value of Redeemable Noncontrolling Interests – Operating Partnership				(14,189)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				2,509				(2,509)
PAID IN CAPITAL
Conversion of OP Units into Common Shares				25
Exercise of share options			1	3,382
Employee Share Purchase Plan (ESPP)				893
RETAINED EARNINGS
Net income attributable to controlling interests	214,937				214,937
Common Share distributions					(198,939)
Preferred Share distributions					(773)
Accumulated other comprehensive income (loss) – derivative instruments:
Unrealized holding gains (losses) arising during the period	12,026					12,026
Losses reclassified into earnings from other comprehensive income	(4,595)					4,595
DISTRIBUTIONS
Distributions declared per Common Share outstanding							0.54
NONCONTROLLING INTERESTS
Conversion of OP Units into Common Shares				25
Equity compensation associated with Noncontrolling Interests								2,958
Net income	223,846
Distributions to Noncontrolling Interests								(7,186)	(1,262)
Change in carrying value of Redeemable Noncontrolling Interests - Operating Partnership								(567)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				2,509				(2,509)
Conversion of OP Units held by Noncontrolling Interests into OP Units held by General Partner								(25)
Net income attributable to Noncontrolling Interests	8,159							8,159	750
PARTIALLY OWNED PROPERTIES
Net income attributable to Noncontrolling Interests	8,159							8,159	750
Distributions to Noncontrolling Interests								(7,186)	(1,262)
Balance, end of period at Sep. 30, 2018		37,280	3,684	8,900,324	1,344,825	(50,689)
Balance, end of period at Sep. 30, 2018								233,825	(2,158)
Balance, beginning of year at Dec. 31, 2018	10,173,204	37,280	3,694	8,935,453	1,261,763	(64,986)
Balance, beginning of year at Dec. 31, 2018	226,445							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 into Common Shares			3	9,840
Equity compensation associated with Noncontrolling Interests								12,200
Net income	708,402
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)
Conversion of OP Units held by Noncontrolling Interests into OP Units held by General Partner								(9,843)
Net income attributable to Noncontrolling Interests	25,339							25,339	2,450
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	10,182,636	37,280	3,713	8,917,312	1,308,423	(84,092)
Balance, end of period at Sep. 30, 2019	224,363							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 into Common Shares			1	4,971
Equity compensation associated with Noncontrolling Interests								1,371
Net income	277,846
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
Conversion of OP Units held by Noncontrolling Interests into OP Units held by General Partner								(4,972)
Net income attributable to Noncontrolling Interests	9,910							9,910	830
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	10,182,636	$ 37,280	$ 3,713	$ 8,917,312	$ 1,308,423	$ (84,092)
Balance, end of period at Sep. 30, 2019	$ 224,363							$ 226,065	$ (1,702)