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				134
Exercise of share options			1	1,599
Employee Share Purchase Plan (ESPP)				1,681
Share-based employee compensation expense:
Restricted shares			1	2,622
Share options				7,338
ESPP discount				297
Offering costs				(26)
Supplemental Executive Retirement Plan (SERP)				83
Change in market value of Redeemable Noncontrolling Interests – Operating Partnership	$ (12,831)			12,831
Adjustment for Noncontrolling Interests ownership in Operating Partnership				(2,839)				2,839
PAID IN CAPITAL
Conversion of OP Units into Common Shares				134
Exercise of share options			1	1,599
Employee Share Purchase Plan (ESPP)				1,681
RETAINED EARNINGS
Net income attributable to controlling interests	211,809				211,809
Common Share distributions					(198,928)
Preferred Share distributions					(773)
Accumulated other comprehensive income (loss) – derivative instruments:
Unrealized holding gains (losses) arising during the period	6,087					6,087
Losses reclassified into earnings from other comprehensive income	(4,791)					4,791
DISTRIBUTIONS
Distributions declared per Common Share outstanding							$ 0.54
NONCONTROLLING INTERESTS
Issuance of restricted units to Noncontrolling Interests								1
Conversion of OP Units into Common Shares				134
Equity compensation associated with Noncontrolling Interests								4,803
Net income	220,548
Distributions to Noncontrolling Interests								(7,188)	(4,220)
Change in carrying value of Redeemable Noncontrolling Interests - Operating Partnership	443							(443)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				(2,839)				2,839
Conversion of OP Units held by Noncontrolling Interests into OP Units held by General Partner								(134)
Net income attributable to Noncontrolling Interests	8,059							8,059	680
PARTIALLY OWNED PROPERTIES
Net income attributable to Noncontrolling Interests	8,059							8,059	680
Contributions by Noncontrolling Interests									125
Distributions to Noncontrolling Interests								(7,188)	(4,220)
Balance, end of period at Mar. 31, 2018		37,280	3,682	8,910,306	1,415,638	(77,734)
Balance, end of period at Mar. 31, 2018								234,628	1,293
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	4,785
Exercise of share options			7	29,853
Employee Share Purchase Plan (ESPP)				1,126
Share-based employee compensation expense:
Restricted shares			2	4,576
Share options				793
ESPP discount				267
Supplemental Executive Retirement Plan (SERP)				(602)
Change in market value of Redeemable Noncontrolling Interests – Operating Partnership	55,021			(55,021)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				4,652				(4,652)
PAID IN CAPITAL
Conversion of OP Units into Common Shares			2	4,785
Exercise of share options			7	29,853
Employee Share Purchase Plan (ESPP)				1,126
RETAINED EARNINGS
Net income attributable to controlling interests	104,539				104,539
Common Share distributions					(210,497)
Preferred Share distributions					(773)
Accumulated other comprehensive income (loss) – derivative instruments:
Unrealized holding gains (losses) arising during the period	(14,420)					(14,420)
Losses reclassified into earnings from other comprehensive income	(4,393)					4,393
DISTRIBUTIONS
Distributions declared per Common Share outstanding							$ 0.5675
NONCONTROLLING INTERESTS
Conversion of OP Units into Common Shares			2	4,785
Equity compensation associated with Noncontrolling Interests								7,903
Net income	109,257
Distributions to Noncontrolling Interests								(7,605)	(3,968)
Change in carrying value of Redeemable Noncontrolling Interests - Operating Partnership	(1,565)							1,565
Adjustment for Noncontrolling Interests ownership in Operating Partnership				4,652				(4,652)
Conversion of OP Units held by Noncontrolling Interests into OP Units held by General Partner								(4,787)
Net income attributable to Noncontrolling Interests	3,919							3,919	799
PARTIALLY OWNED PROPERTIES
Net income attributable to Noncontrolling Interests	3,919							3,919	799
Distributions to Noncontrolling Interests								(7,605)	(3,968)
Balance, end of period at Mar. 31, 2019	10,046,886	$ 37,280	$ 3,705	$ 8,925,882	$ 1,155,032	$ (75,013)
Balance, end of period at Mar. 31, 2019	$ 219,619							$ 225,081	$ (5,462)