Reportable Segments - Reconciliation of NOI from Rental Real Estate Specific to Continuing Operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items]
Rental income	$ 652,677	$ 623,951	$ 1,925,128	$ 1,840,170
Property and maintenance expense	(110,541)	(104,721)	(322,487)	(306,645)
Real estate taxes and insurance expense	(87,388)	(84,087)	(268,784)	(253,318)
Operating income	224,731	217,786	639,254	632,707
Same Store, Non-same Store and Other
Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items]
Rental income	652,677	623,951	1,925,128	1,840,170
Property and maintenance expense	(110,541)	(104,721)	(322,487)	(306,645)
Real estate taxes and insurance expense	(87,388)	(84,087)	(268,784)	(253,318)
Total operating expenses	(197,929)	(188,808)	(591,271)	(559,963)
Operating income	$ 454,748	$ 435,143	$ 1,333,857	$ 1,280,207