Derivatives (Details)	3 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($) instrument	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($) instrument	Dec. 31, 2016 USD ($) instrument	Oct. 31, 2015 USD ($) instrument	May 31, 2014 USD ($) instrument	Apr. 30, 2013 USD ($) instrument
Derivative [Line Items]
Stockholders' equity (deficit)	$ 4,152,887,000	$ 3,864,506,000	$ 4,154,605,000		$ 3,840,910,000
Interest expense	29,957,000	26,602,000
Interest rate cash flow hedge gain (loss) to be reclassified over next 12 months, net	(1,317,000)
Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Interest expense	323,000	$ 525,000
Forward Swap
Derivative [Line Items]
Number of interest rate derivatives terminated | instrument				2		2	2	4	3	4
Aggregate Notional Amount				$ 250,000,000		$ 250,000,000	$ 180,000,000	$ 300,000,000	$ 225,000,000	$ 240,000,000
Liability Fair Value When Terminated						7,690,000		13,369,000	6,312,000	3,156,000
Asset Fair Value When Terminated				(4,080,000)			(13,352,000)
Fair Value Deferred In Other Comprehensive Income				$ (4,080,000)		$ 7,688,000	$ (13,345,000)	$ 13,369,000	$ 6,312,000	$ 3,141,000
Interest rate cash flow hedge
Derivative [Line Items]
Stockholders' equity (deficit)	$ (6,588,000)