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				331
Exercise of share options			1	2,616
Employee Share Purchase Plan (ESPP)			1	2,180
Share-based employee compensation expense:
Restricted shares			1	5,162
Share options				8,536
ESPP discount				400
Offering costs				(27)
Supplemental Executive Retirement Plan (SERP)				(538)
Change in market value of Redeemable Noncontrolling Interests – Operating Partnership	$ 172			(172)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				110				(110)
PAID IN CAPITAL
Conversion of OP Units into Common Shares				331
Exercise of share options			1	2,616
Employee Share Purchase Plan (ESPP)			1	2,180
RETAINED EARNINGS
Net income attributable to controlling interests	325,411				325,411
Common Share distributions					(397,796)
Preferred Share distributions					(1,545)
Accumulated other comprehensive income (loss) – derivative instruments:
Unrealized holding gains (losses) arising during the period	11,995					11,995
Losses reclassified into earnings from other comprehensive income	(9,307)					9,307
DISTRIBUTIONS
Distributions declared per Common Share outstanding							$ 1.08
NONCONTROLLING INTERESTS
Issuance of restricted units to Noncontrolling Interests								1
Conversion of OP Units into Common Shares				331
Equity compensation associated with Noncontrolling Interests								8,116
Net income	338,958
Distributions to Noncontrolling Interests								(14,374)	(7,668)
Change in carrying value of Redeemable Noncontrolling Interests - Operating Partnership	(644)							644
Adjustment for Noncontrolling Interests ownership in Operating Partnership				110				(110)
Conversion of OP Units held by Noncontrolling Interests into OP Units held by General Partner								(331)
Net income attributable to Noncontrolling Interests	12,358							12,358	1,189
PARTIALLY OWNED PROPERTIES
Net income attributable to Noncontrolling Interests	12,358							12,358	1,189
Contributions by Noncontrolling Interests									125
Distributions to Noncontrolling Interests								(14,374)	(7,668)
Balance, end of period at Jun. 30, 2018		37,280	3,683	8,905,184	1,329,600	(67,310)
Balance, end of period at Jun. 30, 2018								232,995	(1,646)
Balance, beginning of year at Mar. 31, 2018		37,280	3,682	8,910,306	1,415,638	(77,734)
Balance, beginning of year at Mar. 31, 2018								234,628	1,293
COMMON SHARES, $0.01 PAR VALUE
Conversion of OP Units into Common Shares				197
Exercise of share options				1,017
Employee Share Purchase Plan (ESPP)			1	499
Share-based employee compensation expense:
Restricted shares				2,540
Share options				1,198
ESPP discount				103
Offering costs				(1)
Supplemental Executive Retirement Plan (SERP)				(621)
Change in market value of Redeemable Noncontrolling Interests – Operating Partnership				(13,003)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				2,949				(2,949)
PAID IN CAPITAL
Conversion of OP Units into Common Shares				197
Exercise of share options				1,017
Employee Share Purchase Plan (ESPP)			1	499
RETAINED EARNINGS
Net income attributable to controlling interests	113,602				113,602
Common Share distributions					(198,868)
Preferred Share distributions					(772)
Accumulated other comprehensive income (loss) – derivative instruments:
Unrealized holding gains (losses) arising during the period	5,908					5,908
Losses reclassified into earnings from other comprehensive income	(4,516)					4,516
DISTRIBUTIONS
Distributions declared per Common Share outstanding							0.54
NONCONTROLLING INTERESTS
Conversion of OP Units into Common Shares				197
Equity compensation associated with Noncontrolling Interests								3,313
Net income	118,410
Distributions to Noncontrolling Interests								(7,186)	(3,448)
Change in carrying value of Redeemable Noncontrolling Interests - Operating Partnership								1,087
Adjustment for Noncontrolling Interests ownership in Operating Partnership				2,949				(2,949)
Conversion of OP Units held by Noncontrolling Interests into OP Units held by General Partner								(197)
Net income attributable to Noncontrolling Interests	4,299							4,299	509
PARTIALLY OWNED PROPERTIES
Net income attributable to Noncontrolling Interests	4,299							4,299	509
Distributions to Noncontrolling Interests								(7,186)	(3,448)
Balance, end of period at Jun. 30, 2018		37,280	3,683	8,905,184	1,329,600	(67,310)
Balance, end of period at Jun. 30, 2018								232,995	(1,646)
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			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 into Common Shares			2	4,869
Equity compensation associated with Noncontrolling Interests								10,829
Net income	430,556
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)
Conversion of OP Units held by Noncontrolling Interests into OP Units held by General Partner								(4,871)
Net income attributable to Noncontrolling Interests	15,429							15,429	1,620
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	10,153,529	37,280	3,708	8,949,581	1,252,809	(89,849)
Balance, end of period at Jun. 30, 2019	226,022							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 into Common Shares				84
Equity compensation associated with Noncontrolling Interests								2,926
Net income	321,299
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)
Conversion of OP Units held by Noncontrolling Interests into OP Units held by General Partner								(84)
Net income attributable to Noncontrolling Interests	11,510							11,510	821
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	10,153,529	$ 37,280	$ 3,708	$ 8,949,581	$ 1,252,809	$ (89,849)
Balance, end of period at Jun. 30, 2019	$ 226,022							$ 227,320	$ (1,298)