Quarterly Results of Operations (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 112,317	$ 110,428	$ 92,097	$ 81,805	$ 98,077	$ 91,567	$ 84,545	$ 76,361	$ 396,647	$ 350,550	$ 308,679
Gross profit	88,032	86,826	72,393	64,883	77,037	72,403	67,604	59,498	312,134	276,542	243,007
Net income	$ 16,676	$ 17,294	$ 9,883	$ 5,253	$ 14,553	$ 11,138	$ 9,910	$ 5,008	$ 49,106	$ 40,609	$ 32,428
Diluted net income per share (in dollars per share)	$ 0.40	$ 0.41	$ 0.24	$ 0.12	$ 0.34	$ 0.26	$ 0.23	$ 0.12	$ 1.17	$ 0.96	$ 0.76