Long-term debt Schedule of Derivative Instruments (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 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
Derivative Asset, Fair Value, Gross Asset	$ 70,000		$ 851,000
Term Loan Facility | Interest Rate Cap One | Maximum
Derivative [Line Items]
Notional amounts of interest rate agreements	$ 3,500,000,000
LIBOR plus interest rate margin	3.50%
Cash Flow Hedging
Derivative [Line Items]
Amount of losses reclassified from accumulated OCI into income	$ (1,606,000)	$ (1,537,000)
Amount of unrecognized (losses) gains in OCI on interest rate cap agreements	580,000	(1,050,000)
Debt Expense | Cash Flow Hedging | Interest rate cap agreements
Derivative [Line Items]
Amount of losses reclassified from accumulated OCI into income	(2,163,000)	(2,070,000)
Amount of unrecognized (losses) gains in OCI on interest rate cap agreements	$ 781,000	$ (1,414,000)