Long-term debt - Effects of Interest Rate Swap and Cap Agreements (Detail) - Cash Flow Hedging - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Derivative Instruments Gain Loss [Line Items]
Amount of unrecognized (losses) gains in OCI on interest rate cap agreements	$ (31)	$ (268)	$ (611)	$ 782
Reclassification from accumulated other comprehensive income into net income	1,606	1,537	3,212	3,074
Tax benefit (expense)
Derivative Instruments Gain Loss [Line Items]
Amount of unrecognized (losses) gains in OCI on interest rate cap agreements	11	93	212	(271)
Reclassification from accumulated other comprehensive income into net income	(557)	(533)	(1,114)	(1,066)
Interest rate cap agreements | Debt Expense
Derivative Instruments Gain Loss [Line Items]
Amount of unrecognized (losses) gains in OCI on interest rate cap agreements	(42)	(361)	(823)	1,053
Reclassification from accumulated other comprehensive income into net income	$ 2,163	$ 2,070	$ 4,326	$ 4,140