Summary of Unaudited Quarterly Results of Operations (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended												12 Months Ended
	Mar. 31, 2015		Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2015		Mar. 31, 2014	Mar. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 67,557		$ 62,005		$ 51,938		$ 48,811		$ 50,433	$ 46,195	$ 44,345	$ 42,670	$ 230,311		$ 183,643	$ 158,124
Cost of product revenue	10,806		9,838		9,612		9,689		10,114	9,458	9,027	8,723	39,945		37,322	31,596
Other operating expenses	44,388		38,504		38,148		40,660		36,641	32,143	33,920	35,254	161,700		137,958
Other income (expense), net	9		38		(3)		55		84	57	31	(5)	99		167	319
Income (loss) before income taxes	12,372		13,701		4,175		(1,483)		3,762	4,651	1,429	(1,312)	28,765		8,530	16,862
Income tax (benefit) provision	(86,502)	[1]	1,017	[1]	336	[1]	226	[1]	140	258	370	411	(84,923)	[1]	1,179	1,848
Net income (loss)	$ 98,874		$ 12,684		$ 3,839		$ (1,709)		$ 3,622	$ 4,393	$ 1,059	$ (1,723)	$ 113,688		$ 7,351	$ 15,014
Basic net income (loss) per share	$ 2.40		$ 0.31		$ 0.09		$ (0.04)		$ 0.09	$ 0.11	$ 0.03	$ (0.04)	$ 2.80		$ 0.19	$ 0.38
Diluted net income (loss) per share	$ 2.24		$ 0.30		$ 0.09		$ (0.04)		$ 0.09	$ 0.11	$ 0.03	$ (0.04)	$ 2.65		$ 0.18	$ 0.37

[1] Net income for the quarter and year ended March 31, 2015 included an income tax benefit of $84.9 million, primarily due to the release of the valuation allowance on certain deferred tax assets in the quarter ended March 31, 2015.