Long-term debt Schedule of Derivative Instruments (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Interest Rate Cap Agreements Effective June 29, 2018
Derivative [Line Items]
Derivative, effective date			Jun. 29, 2018
Derivative, expiration date			Jun. 30, 2020
Interest Rate Cap Agreements Effective August 12, 2019
Derivative [Line Items]
Derivative, effective date			Jun. 30, 2020
Derivative, expiration date			Jun. 30, 2024
Term Loan Facility | Interest Rate Cap Agreements Effective June 29, 2018 | Maximum
Derivative [Line Items]
Notional amounts of interest rate agreements	$ 3,500,000,000		$ 3,500,000,000
LIBOR plus interest rate margin			3.50%
Term Loan Facility | Interest Rate Cap Agreements Effective August 12, 2019 | Maximum
Derivative [Line Items]
Notional amounts of interest rate agreements	3,500,000,000		$ 3,500,000,000
LIBOR plus interest rate margin			2.00%
Cash Flow Hedging
Derivative [Line Items]
Amount of losses reclassified from accumulated OCI into income	(1,569,000)	$ (1,606,000)	$ (4,782,000)	$ (4,680,000)
Amount of unrecognized (losses) gains in OCI on interest rate cap agreements	1,060,000	$ (37,000)	1,672,000	$ (819,000)
Debt Expense | Cash Flow Hedging | Interest Rate Cap Agreements Effective June 29, 2018
Derivative [Line Items]
Amount of losses reclassified from accumulated OCI into income			(6,428,000)
Amount of unrecognized (losses) gains in OCI on interest rate cap agreements			851,000
Debt Expense | Cash Flow Hedging | Interest Rate Cap Agreements Effective August 12, 2019
Derivative [Line Items]
Amount of unrecognized (losses) gains in OCI on interest rate cap agreements			1,393,000
Other Long-term Assets | Interest Rate Cap Agreements Effective June 29, 2018
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	0		0		$ 851,000
Other Long-term Assets | Interest Rate Cap Agreements Effective August 12, 2019
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 20,642,000		$ 20,642,000