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			2	4,869
Exercise of share options			10	48,477
Employee Share Purchase Plan (ESPP)				1,652
Share-based employee compensation expense:
Restricted shares			2	7,980
Share options				1,682
ESPP discount				365
Offering costs				(155)
Supplemental Executive Retirement Plan (SERP)				(1,539)
Change in market value of Redeemable Noncontrolling Interests –Operating Partnership	$ 56,974			(56,974)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				7,771				(7,771)
PAID IN CAPITAL
Conversion of OP Units into Common Shares			2	4,869
Exercise of share options			10	48,477
Employee Share Purchase Plan (ESPP)				1,652
RETAINED EARNINGS
Net income attributable to controlling interests	413,507				413,507
Common Share distributions					(420,916)
Preferred Share distributions					(1,545)
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	(8,902)					8,902
DISTRIBUTIONS
Distributions declared per Common Share outstanding							$ 1.135
NONCONTROLLING INTERESTS
Conversion of OP Units held by Noncontrolling Interests into OP Units held by General Partner								(4,871)
Equity compensation associated with Noncontrolling Interests								10,829
Net income attributable to Noncontrolling Interests	15,429							15,429	1,620
Distributions to Noncontrolling Interests								(15,079)	(5,219)
Change in carrying value of Redeemable Noncontrolling Interests – Operating Partnership	(45)							45
Adjustment for Noncontrolling Interests ownership in Operating Partnership				7,771				(7,771)
PARTIALLY OWNED PROPERTIES
Net income attributable to Noncontrolling Interests	15,429							15,429	1,620
Contributions by Noncontrolling Interests									4,594
Distributions to Noncontrolling Interests								(15,079)	(5,219)
Balance, end of period at Jun. 30, 2019		37,280	3,708	8,949,581	1,252,809	(89,849)
Balance, end of period at Jun. 30, 2019								227,320	(1,298)
Balance, beginning of year at Mar. 31, 2019		37,280	3,705	8,925,882	1,155,032	(75,013)
Balance, beginning of year at Mar. 31, 2019								225,081	(5,462)
COMMON SHARES, $0.01 PAR VALUE
Conversion of OP Units into Common Shares				84
Exercise of share options			3	18,624
Employee Share Purchase Plan (ESPP)				526
Share-based employee compensation expense:
Restricted shares				3,404
Share options				889
ESPP discount				98
Offering costs				(155)
Supplemental Executive Retirement Plan (SERP)				(937)
Change in market value of Redeemable Noncontrolling Interests –Operating Partnership				(1,953)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				3,119				(3,119)
PAID IN CAPITAL
Conversion of OP Units into Common Shares				84
Exercise of share options			3	18,624
Employee Share Purchase Plan (ESPP)				526
RETAINED EARNINGS
Net income attributable to controlling interests	308,968				308,968
Common Share distributions					(210,419)
Preferred Share distributions					(772)
Accumulated other comprehensive income (loss) - derivative instruments:
Unrealized holding gains (losses) arising during the period	(19,345)					(19,345)
Losses reclassified into earnings from other comprehensive income	(4,509)					4,509
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								(84)
Equity compensation associated with Noncontrolling Interests								2,926
Net income attributable to Noncontrolling Interests	11,510							11,510	821
Distributions to Noncontrolling Interests								(7,474)	(1,251)
Change in carrying value of Redeemable Noncontrolling Interests – Operating Partnership								(1,520)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				3,119				(3,119)
PARTIALLY OWNED PROPERTIES
Net income attributable to Noncontrolling Interests	11,510							11,510	821
Contributions by Noncontrolling Interests									4,594
Distributions to Noncontrolling Interests								(7,474)	(1,251)
Balance, end of period at Jun. 30, 2019		37,280	3,708	8,949,581	1,252,809	(89,849)
Balance, end of period at Jun. 30, 2019								227,320	(1,298)
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	3,855
Exercise of share options			2	11,320
Employee Share Purchase Plan (ESPP)				2,359
Share-based employee compensation expense:
Restricted shares			2	7,252
Share options				1,293
ESPP discount				416
Supplemental Executive Retirement Plan (SERP)				(506)
Change in market value of Redeemable Noncontrolling Interests –Operating Partnership	(128,753)			128,753
Adjustment for Noncontrolling Interests ownership in Operating Partnership				(1,987)				1,987
PAID IN CAPITAL
Conversion of OP Units into Common Shares			1	3,855
Exercise of share options			2	11,320
Employee Share Purchase Plan (ESPP)				2,359
RETAINED EARNINGS
Net income attributable to controlling interests	569,494				569,494
Common Share distributions					(448,750)
Preferred Share distributions					(1,545)
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	(11,398)					11,398
DISTRIBUTIONS
Distributions declared per Common Share outstanding							1.205
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								(3,856)
Equity compensation associated with Noncontrolling Interests								7,026
Net income attributable to Noncontrolling Interests	21,248							21,248	13,410
Distributions to Noncontrolling Interests								(17,037)	(10,300)
Change in carrying value of Redeemable Noncontrolling Interests – Operating Partnership	2,048							(2,048)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				(1,987)				1,987
PARTIALLY OWNED PROPERTIES
Net income attributable to Noncontrolling Interests	21,248							21,248	13,410
Contributions by Noncontrolling Interests									341
Distributions to Noncontrolling Interests								(17,037)	(10,300)
Balance, end of period at Jun. 30, 2020	10,597,673	37,280	3,722	9,118,332	1,505,694	(67,355)
Balance, end of period at Jun. 30, 2020	239,803							235,169	4,634
Balance, beginning of year at Mar. 31, 2020		37,280	3,721	9,092,441	1,469,821	(72,896)
Balance, beginning of year at Mar. 31, 2020								235,580	4,739
COMMON SHARES, $0.01 PAR VALUE
Conversion of OP Units into Common Shares			1	2,011
Exercise of share options				171
Employee Share Purchase Plan (ESPP)				1,490
Share-based employee compensation expense:
Restricted shares				3,231
Share options				623
ESPP discount				263
Supplemental Executive Retirement Plan (SERP)				(655)
Change in market value of Redeemable Noncontrolling Interests –Operating Partnership				17,304
Adjustment for Noncontrolling Interests ownership in Operating Partnership				1,453				(1,453)
PAID IN CAPITAL
Conversion of OP Units into Common Shares			1	2,011
Exercise of share options				171
Employee Share Purchase Plan (ESPP)				1,490
RETAINED EARNINGS
Net income attributable to controlling interests	260,888				260,888
Common Share distributions					(224,243)
Preferred Share distributions					(772)
Accumulated other comprehensive income (loss) - derivative instruments:
Unrealized holding gains (losses) arising during the period	(223)					(223)
Losses reclassified into earnings from other comprehensive income	(5,764)					5,764
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								(2,012)
Equity compensation associated with Noncontrolling Interests								1,959
Net income attributable to Noncontrolling Interests	9,713							9,713	880
Distributions to Noncontrolling Interests								(7,961)	(985)
Change in carrying value of Redeemable Noncontrolling Interests – Operating Partnership								(657)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				1,453				(1,453)
PARTIALLY OWNED PROPERTIES
Net income attributable to Noncontrolling Interests	9,713							9,713	880
Distributions to Noncontrolling Interests								(7,961)	(985)
Balance, end of period at Jun. 30, 2020	10,597,673	$ 37,280	$ 3,722	$ 9,118,332	$ 1,505,694	$ (67,355)
Balance, end of period at Jun. 30, 2020	$ 239,803							$ 235,169	$ 4,634