Quarterly Financial Data - Summary of Quarterly Results (Detail) - USD ($) $ / shares in Units, $ 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, net	$ 177,274	$ 171,200	$ 170,478	$ 167,036	$ 165,858	$ 163,503	$ 155,621	$ 143,510	$ 685,988	$ 628,492	$ 499,278
Gross profit	61,490	59,433	58,452	58,657	59,742	60,305	55,143	50,385	238,032	225,575	166,743
Net income	$ 15,488	$ 16,050	$ 16,375	$ 13,820	$ 14,762	$ 15,162	$ 12,074	$ 9,567	$ 61,733	$ 51,565	$ 32,445
Earnings Per Share:
Basic (in dollars per share)	$ 0.46	$ 0.48	$ 0.49	$ 0.41	$ 0.44	$ 0.46	$ 0.36	$ 0.29	$ 1.84	$ 1.55	$ 0.99
Diluted (in dollars per share)	$ 0.45	$ 0.46	$ 0.47	$ 0.40	$ 0.43	$ 0.44	$ 0.35	$ 0.28	$ 1.79	$ 1.51	$ 0.96
Weighted-average number of shares used in computing earnings per share:
Basic (in shares)	33,638,170	33,624,401	33,621,444	33,380,028	33,231,716	33,307,312	33,417,079	33,236,259	33,566,367	33,298,104	32,804,606
Diluted (in shares)	34,714,308	34,675,485	34,510,400	34,351,657	34,272,731	34,180,635	34,207,973	34,051,971	34,563,319	34,178,340	33,636,593
Stock compensation expense	$ 5,027	$ 4,484	$ 4,450	$ 5,809	$ 3,768	$ 4,471	$ 3,553	$ 4,255	$ 19,770	$ 16,047	$ 11,011
Amortization of intangibles	$ 3,592	$ 2,848	$ 2,718	$ 2,715	$ 2,717	$ 2,642	$ 2,808	$ 2,059	$ 11,873	$ 10,226	$ 6,623