CONSOLIDATED STATEMENT 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)	OPERATING PARTNERSHIP	PARTIALLY OWNED PROPERTIES
Balance, beginning of year at Dec. 31, 2014		$ 50,000	$ 3,629	$ 8,536,340	$ 1,950,639	$ (172,152)
Balance, beginning of year at Dec. 31, 2014							$ 214,411	$ 124,909
PREFERRED SHARES
Partial redemption of 8.29% Series K Cumulative Redeemable		(12,720)
COMMON SHARES, $0.01 PAR VALUE
Conversion of OP Units into Common Shares			2	4,964
Exercise of share options			14	59,494
Employee Share Purchase Plan (ESPP)			1	4,403
Restricted shares			2	15,064
Share options				3,756
ESPP discount				884
PAID IN CAPITAL
Conversion of OP Units into Common Shares			2	4,964
Exercise of share options			14	59,494
Employee Share Purchase Plan (ESPP)			1	4,403
Conversion of restricted shares to restricted units				70			70
Share-based employee compensation expense:
Offering costs				(79)
Supplemental Executive Retirement Plan (SERP)				1,380
Change in market value of Redeemable Noncontrolling Interests – Operating Partnership	$ 64,378			(64,378)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				10,607			(10,607)
Conversion of restricted shares to restricted units				(70)			(70)
RETAINED EARNINGS
Net income attributable to controlling interests	870,120				870,120
Common Share distributions					(804,825)
Preferred Share distributions					(3,357)
Premium on redemption of Preferred Shares - cash charge					(3,486)
ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)
Unrealized holding gains (losses) arising during the year	2,219					2,219
Losses reclassified into earnings from other comprehensive income	(18,244)					18,244
Currency translation adjustments arising during the year	(327)					(327)
Balance, beginning of year at Dec. 31, 2014							214,411	124,909
OPERATING PARTNERSHIP
Issuance of restricted units to Noncontrolling Interests							3
Conversion of OP Units held by Noncontrolling Interests into OP Units held by General Partner							(4,966)
Conversion of restricted shares to restricted units				70			70
Equity compensation associated with Noncontrolling Interests							21,503
Net income attributable to Noncontrolling Interests	34,241						34,241	3,657
Distributions to Noncontrolling Interests							(31,604)	(6,608)
Change in carrying value of Redeemable Noncontrolling Interests – Operating Partnership	1,672						(1,672)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				10,607			(10,607)
PARTIALLY OWNED PROPERTIES
Net income attributable to Noncontrolling Interests	34,241						34,241	3,657
Distributions to Noncontrolling Interests							(31,604)	(6,608)
Deconsolidation of previously consolidated Noncontrolling Interests								(117,350)
Balance, end of period at Dec. 31, 2015		37,280	3,648	8,572,365	2,009,091	(152,016)
Balance, end of period at Dec. 31, 2015							221,379	4,608
COMMON SHARES, $0.01 PAR VALUE
Conversion of OP Units into Common Shares			1	3,725
Exercise of share options			8	35,825
Employee Share Purchase Plan (ESPP)			1	3,685
Restricted shares			1	15,015
Share options				3,432
ESPP discount				650
PAID IN CAPITAL
Conversion of OP Units into Common Shares			1	3,725
Exercise of share options			8	35,825
Employee Share Purchase Plan (ESPP)			1	3,685
Share-based employee compensation expense:
Offering costs				(314)
Supplemental Executive Retirement Plan (SERP)				748
Change in market value of Redeemable Noncontrolling Interests – Operating Partnership	(115,093)			115,093
Adjustment for Noncontrolling Interests ownership in Operating Partnership				8,198			(8,198)
RETAINED EARNINGS
Net income attributable to controlling interests	4,292,163				4,292,163
Common Share distributions					(4,754,537)
Preferred Share distributions					(3,091)
ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)
Unrealized holding gains (losses) arising during the year	(3,915)					(3,915)
Losses reclassified into earnings from other comprehensive income	(41,758)					41,758
Currency translation adjustments arising during the year	264					264
Balance, beginning of year at Dec. 31, 2015							221,379	4,608
OPERATING PARTNERSHIP
Issuance of restricted units to Noncontrolling Interests							1
Conversion of OP Units held by Noncontrolling Interests into OP Units held by General Partner							(3,726)
Equity compensation associated with Noncontrolling Interests							18,180
Net income attributable to Noncontrolling Interests	171,511						171,511	16,430
Distributions to Noncontrolling Interests							(187,448)	(36,268)
Change in carrying value of Redeemable Noncontrolling Interests – Operating Partnership	(9,598)						9,598
Adjustment for Noncontrolling Interests ownership in Operating Partnership				8,198			(8,198)
PARTIALLY OWNED PROPERTIES
Net income attributable to Noncontrolling Interests	171,511						171,511	16,430
Distributions to Noncontrolling Interests							(187,448)	(36,268)
Other								25,839
Balance, end of period at Dec. 31, 2016	10,229,078	37,280	3,659	8,758,422	1,543,626	(113,909)
Balance, end of period at Dec. 31, 2016	231,906						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
Share-based employee compensation expense:
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)
ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)
Unrealized holding gains (losses) arising during the year	6,439					6,439
Losses reclassified into earnings from other comprehensive income	(18,858)					18,858
Currency translation adjustments arising during the year	0
Balance, beginning of year at Dec. 31, 2016	231,906						221,297	10,609
OPERATING PARTNERSHIP
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	10,242,464	$ 37,280	$ 3,680	$ 8,886,586	$ 1,403,530	$ (88,612)
Balance, end of period at Dec. 31, 2017	$ 231,399						$ 226,691	$ 4,708