Long-term debt - Effects of Interest Rate Swap and Cap Agreements (Detail) - Cash Flow Hedging - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Derivative Instruments Gain Loss [Line Items]
Amount of unrecognized (losses) gains in OCI on interest rate cap agreements	$ (580)	$ 1,050
Reclassification from accumulated other comprehensive income into net income	1,606	1,537
Tax benefit (expense)
Derivative Instruments Gain Loss [Line Items]
Amount of unrecognized (losses) gains in OCI on interest rate cap agreements	201	(364)
Reclassification from accumulated other comprehensive income into net income	(557)	(533)
Interest rate cap agreements | Debt Expense
Derivative Instruments Gain Loss [Line Items]
Amount of unrecognized (losses) gains in OCI on interest rate cap agreements	(781)	1,414
Reclassification from accumulated other comprehensive income into net income	$ 2,163	$ 2,070