CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - 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, 2016		$ 37,280	$ 3,659	$ 8,758,422	$ 1,543,626	$ (113,909)
Balance, beginning of year at Dec. 31, 2016								$ 221,297	$ 10,609
COMMON SHARES, $0.01 PAR VALUE
Conversion of OP Units into Common Shares			11	15,889
Exercise of share options			8	31,588
Employee Share Purchase Plan (ESPP)			1	3,743
Restricted shares			1	9,776
Share options				6,835
ESPP discount				747
PAID IN CAPITAL
Conversion of OP Units into Common Shares			11	15,889
Exercise of share options			8	31,588
Employee Share Purchase Plan (ESPP)			1	3,743
Offering costs				(51)
Supplemental Executive Retirement Plan (SERP)				(594)
Change in market value of Redeemable Noncontrolling Interests – Operating Partnership	$ (41,916)			41,916
Adjustment for Noncontrolling Interests ownership in Operating Partnership				18,315				(18,315)
RETAINED EARNINGS
Net income attributable to controlling interests	603,454				603,454
Common Share distributions					(740,459)
Preferred Share distributions					(3,091)
Unrealized holding gains (losses) arising during the year	6,439					6,439
Losses reclassified into earnings from other comprehensive income	(18,858)					18,858
DISTRIBUTIONS
Distributions declared per Common Share outstanding							$ 2.015
NONCONTROLLING INTERESTS
Conversion of OP Units held by Noncontrolling Interests into OP Units held by General Partner								(15,900)
Equity compensation associated with Noncontrolling Interests								10,523
Net income attributable to Noncontrolling Interests	22,604							22,604	2,323
Distributions to Noncontrolling Interests								(26,739)	(8,349)
Change in carrying value of Redeemable Noncontrolling Interests – Operating Partnership	(33,221)							33,221
Adjustment for Noncontrolling Interests ownership in Operating Partnership				18,315				(18,315)
PARTIALLY OWNED PROPERTIES
Net income attributable to Noncontrolling Interests	22,604							22,604	2,323
Contributions by Noncontrolling Interests									125
Distributions to Noncontrolling Interests								(26,739)	(8,349)
Balance, end of period at Dec. 31, 2017		37,280	3,680	8,886,586	1,403,530	(88,612)
Balance, end of period at Dec. 31, 2017								226,691	4,708
PARTIALLY OWNED PROPERTIES
Conversion of OP Units into Common Shares			11	15,889
Exercise of share options			8	31,588
Employee Share Purchase Plan (ESPP)			1	3,743
Conversion of OP Units into Common Shares			1	4,097
Exercise of share options			11	30,644
Employee Share Purchase Plan (ESPP)			1	3,878
Restricted shares			1	8,257
Share options				9,734
ESPP discount				767
Conversion of OP Units into Common Shares			1	4,097
Exercise of share options			11	30,644
Employee Share Purchase Plan (ESPP)			1	3,878
Offering costs				(27)
Supplemental Executive Retirement Plan (SERP)				(454)
Change in market value of Redeemable Noncontrolling Interests – Operating Partnership	13,922			(13,922)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				5,893				(5,893)
Net income attributable to controlling interests	657,535				657,535
Common Share distributions					(796,212)
Preferred Share distributions					(3,090)
Unrealized holding gains (losses) arising during the year	5,174					5,174
Losses reclassified into earnings from other comprehensive income	(18,452)					18,452
Distributions declared per Common Share outstanding							2.16
Issuance of restricted units to Noncontrolling Interests								1
Conversion of OP Units held by Noncontrolling Interests into OP Units held by General Partner								(4,098)
Equity compensation associated with Noncontrolling Interests								14,009
Net income attributable to Noncontrolling Interests	24,939							24,939	2,718
Distributions to Noncontrolling Interests								(28,682)	(9,831)
Change in carrying value of Redeemable Noncontrolling Interests – Operating Partnership	(1,771)							1,771
Adjustment for Noncontrolling Interests ownership in Operating Partnership				5,893				(5,893)
Net income attributable to Noncontrolling Interests	24,939							24,939	2,718
Acquisition Noncontrolling Interests Partially Owned Properties									(13)
Contributions by Noncontrolling Interests									125
Distributions to Noncontrolling Interests								(28,682)	(9,831)
Balance, end of period at Dec. 31, 2018	10,173,204	37,280	3,694	8,935,453	1,261,763	(64,986)
Balance, end of period at Dec. 31, 2018	226,445							228,738	(2,293)
PARTIALLY OWNED PROPERTIES
Conversion of OP Units into Common Shares			1	4,097
Exercise of share options			11	30,644
Employee Share Purchase Plan (ESPP)			1	3,878
Conversion of OP Units into Common Shares			3	10,407
Exercise of share options			17	77,768
Employee Share Purchase Plan (ESPP)			1	3,115
Restricted shares			2	12,436
Share options				2,675
ESPP discount				642
Conversion of OP Units into Common Shares			3	10,407
Exercise of share options			17	77,768
Employee Share Purchase Plan (ESPP)			1	3,115
Offering costs				(991)
Supplemental Executive Retirement Plan (SERP)				(1,675)
Change in market value of Redeemable Noncontrolling Interests – Operating Partnership	82,283			(82,283)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				8,030				(8,030)
Net income attributable to controlling interests	970,377				970,377
Common Share distributions					(842,555)
Preferred Share distributions					(3,090)
Unrealized holding gains (losses) arising during the year	(33,765)					(33,765)
Losses reclassified into earnings from other comprehensive income	(21,188)					21,188
Distributions declared per Common Share outstanding							$ 2.27
Issuance of restricted units to Noncontrolling Interests								2
Conversion of OP Units held by Noncontrolling Interests into OP Units held by General Partner								(10,410)
Equity compensation associated with Noncontrolling Interests								13,410
Net income attributable to Noncontrolling Interests	36,034							36,034	3,297
Distributions to Noncontrolling Interests								(29,896)	(7,158)
Change in carrying value of Redeemable Noncontrolling Interests – Operating Partnership	2,011							(2,011)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				8,030				(8,030)
Net income attributable to Noncontrolling Interests	36,034							36,034	3,297
Contributions by Noncontrolling Interests									7,337
Distributions to Noncontrolling Interests								(29,896)	(7,158)
Balance, end of period at Dec. 31, 2019	10,315,506	$ 37,280	3,717	8,965,577	$ 1,386,495	$ (77,563)
Balance, end of period at Dec. 31, 2019	$ 229,020							$ 227,837	$ 1,183
PARTIALLY OWNED PROPERTIES
Conversion of OP Units into Common Shares			3	10,407
Exercise of share options			17	77,768
Employee Share Purchase Plan (ESPP)			$ 1	$ 3,115