Long-Term Debt - Interest Rate Cap and Swap Agreement (Details) - USD ($)	6 Months Ended		12 Months Ended
	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Debt expense recognized			$ 461,897,000	$ 406,341,000	$ 394,013,000
Weighted average effective interest rate at period end	5.19%		5.19%
Weighted average effective interest rate during the period			4.96%
Interest Rate Cap Agreements Effective September 30, 2016
Derivative [Line Items]
Derivative, expiration date		Jun. 30, 2018
Debt expense recognized			$ 4,140,000
Interest Rate Cap Agreements Effective June 29, 2018
Derivative [Line Items]
Derivative, effective date			Jun. 29, 2018
Derivative, expiration date			Jun. 30, 2020
Fair value of assets	$ 851,000		$ 851,000
Debt expense recognized			4,327,000
Amount of unrealized losses in OCI on interest rate cap and swap agreements			(181,000)
Term Loan B | Maximum | Interest rate cap agreements 1
Derivative [Line Items]
Derivative Asset, Notional Amount		$ 3,500,000,000
Term Loan Facility | Maximum | Interest rate cap agreements 1
Derivative [Line Items]
Derivative Asset, Notional Amount	$ 3,500,000,000		$ 3,500,000,000
Debt instrument, variable interest rate margin	3.50%	3.50%
Senior Secured Credit Facilities
Derivative [Line Items]
Weighted average effective interest rate at period end	5.11%		5.11%