Long-term debt - Effects of Interest Rate Swap and Cap Agreements (Detail) - Cash Flow Hedging - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative Instruments Gain Loss [Line Items]
Amount of unrecognized (losses) gains in OCI on interest rate cap agreements	$ (1,060)	$ 37	$ (1,672)	$ 819
Reclassification from accumulated other comprehensive income into net income	1,569	1,606	4,782	4,680
Tax benefit (expense)
Derivative Instruments Gain Loss [Line Items]
Amount of unrecognized (losses) gains in OCI on interest rate cap agreements	360	(13)	572	(284)
Reclassification from accumulated other comprehensive income into net income	(532)	(557)	(1,646)	(1,623)
Interest rate cap agreements | Debt Expense
Derivative Instruments Gain Loss [Line Items]
Amount of unrecognized (losses) gains in OCI on interest rate cap agreements	(1,420)	50	(2,244)	1,103
Reclassification from accumulated other comprehensive income into net income	$ 2,101	$ 2,163	$ 6,428	$ 6,303