Summary of Unaudited Quarterly Results of Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Disclosure Unaudited Quarterly Financial Information [Abstract]
Total revenues	$ 124,680	$ 114,674	$ 102,955	$ 102,995	$ 93,957	$ 85,795	$ 76,359	$ 73,432	$ 445,304	$ 329,543	$ 230,311
Cost of product revenue	19,261	18,987	17,309	15,070	14,663	12,744	12,144	10,868	70,627	50,419	39,945
Other operating expenses	76,425	70,284	71,138	66,692	59,481	55,608	51,398	47,533	284,539	214,020
Other income (expense), net	362	423	228	192	414	55	149	116	1,205	734	99
Income before income taxes	29,356	25,826	14,736	21,425	20,227	17,498	12,966	15,147	91,343	65,838	28,765
Income tax (benefit) provision	14,457	10,394	5,861	8,515	9,229	6,943	5,231	6,288	39,227	27,691	(84,923)
Net income	$ 14,899	$ 15,432	$ 8,875	$ 12,910	$ 10,998	$ 10,555	$ 7,735	$ 8,859	$ 52,116	$ 38,147	$ 113,688
Basic net income per share	$ 0.34	$ 0.36	$ 0.21	$ 0.30	$ 0.26	$ 0.25	$ 0.18	$ 0.21	$ 1.21	$ 0.90	$ 2.80
Diluted net income per share	$ 0.33	$ 0.34	$ 0.20	$ 0.29	$ 0.24	$ 0.23	$ 0.17	$ 0.20	$ 1.17	$ 0.85	$ 2.65