Quarterly Financial Information - Summary of Selected Financial Information (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 158,916	$ 150,845	$ 146,295	$ 134,966	$ 127,440	$ 128,664	$ 124,371	$ 112,626	$ 591,022	$ 493,101	$ 416,643
Gross profit	73,222	71,833	68,253	63,879	60,491	61,792	58,558	52,530	277,187	233,371	193,203
Income before income taxes	19,540	31,744	29,781	27,359	24,760	26,698	23,406	19,603
Net income	$ 8,618	$ 20,142	$ 18,836	$ 17,273	$ 15,317	$ 17,000	$ 14,740	$ 11,883	$ 64,869	$ 58,940	$ 39,101
Earnings per diluted share	$ 0.23	$ 0.55	$ 0.52	$ 0.48	$ 0.43	$ 0.48	$ 0.42	$ 0.33	$ 1.77	$ 1.66	$ 1.13
Shares used in computing diluted earnings per share	37,864	36,349	36,097	35,895	35,661	35,284	35,161	35,500	36,552	35,401	34,590