Quarterly Financial Information (unaudited) - Summary of Selected Financial Information (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 193,281	$ 194,497	$ 188,972	$ 179,293	$ 158,916	$ 150,845	$ 146,295	$ 134,966	$ 756,043	$ 591,022	$ 493,101
Gross profit	92,817	93,480	86,936	82,118	73,222	71,833	68,253	63,879	355,351	277,187	233,371
Income before income taxes (a)	35,119	36,419	30,195	27,574	19,540	31,744	29,781	27,359
Net income	$ 31,196	$ 35,430	$ 25,007	$ 18,224	$ 8,618	$ 20,142	$ 18,836	$ 17,273	$ 109,857	$ 64,869	$ 58,940
Earnings per diluted share	$ 0.80	$ 0.91	$ 0.65	$ 0.47	$ 0.23	$ 0.55	$ 0.52	$ 0.48	$ 2.82	$ 1.77	$ 1.66
Shares used in computing diluted earnings per share (a)	38,975	39,062	38,738	39,071	37,864	36,349	36,097	35,895	38,961	36,552	35,401