Segments - Reconciliation of Total Segment EBITDA to Income Before Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting [Abstract]
Total Segment EBITDA	$ 56,928	$ 45,211	$ 104,503	$ 86,899
Depreciation and amortization	8,619	7,894	17,084	15,845
Other expense	(502)	(933)	(310)	(251)
Income from operations	48,811	38,250	87,729	71,305
Interest expense, net	(8,628)	(9,028)	(17,361)	(17,791)
Income before income taxes	$ 39,681	$ 28,289	$ 70,058	$ 53,263