Quarterly Financial Information - Summary of Selected Financial Information (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 110,735	$ 107,021	$ 103,088	$ 95,799	$ 95,368	$ 93,845	$ 91,368	$ 82,723	$ 416,643	$ 363,304	$ 309,391
Gross profit	52,767	49,549	47,042	43,845	44,640	44,944	40,699	37,419	193,203	167,702	141,912
Income before income taxes	19,062	17,572	15,053	14,132	15,035	17,810	11,682	9,341	65,819	53,868	44,113
Net income	$ 10,512	$ 11,049	$ 9,047	$ 8,493	$ 9,376	$ 10,832	$ 7,105	$ 5,681	$ 39,101	$ 32,994	$ 27,557
Earnings per diluted share	$ 0.30	$ 0.32	$ 0.26	$ 0.25	$ 0.28	$ 0.33	$ 0.22	$ 0.17	$ 1.13	$ 1.00	$ 0.83
Shares used in computing diluted earnings per share	35,348	34,764	34,290	33,948	33,421	32,986	32,769	32,530	34,590	32,916	33,154