Reportable Segments - Reconciliation of NOI from Rental Real Estate Specific to Continuing Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items]
Rental income	$ 2,577,681	$ 2,470,689	$ 2,422,233
Property and maintenance expense	(429,335)	(405,281)	(406,823)
Real estate taxes and insurance expense	(357,814)	(335,495)	(317,387)
Operating income	858,560	847,471	856,086
Same Store, Non-same Store and Other
Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items]
Rental income	2,577,681	2,470,689	2,422,233
Property and maintenance expense	(429,335)	(405,281)	(406,823)
Real estate taxes and insurance expense	(357,814)	(335,495)	(317,387)
Total operating expenses	(787,149)	(740,776)	(724,210)
Operating income	$ 1,790,532	$ 1,729,913	$ 1,698,023