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, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
Quarterly Financial Data [Line Items]
Total revenues	$ 43,674	$ 38,250	$ 37,417	$ 38,783	$ 37,344	$ 32,198	$ 29,478	$ 27,355	$ 158,124	$ 126,375	$ 101,151
Cost of product revenue	8,826	8,130	7,194	7,446	6,786	6,279	5,551	5,891	31,596	24,507	21,977
Other operating expenses	30,716	27,202	24,291	27,776	27,616	23,686	23,161	25,885	109,985	100,348
Other income (expense), net	8	325	(8)	(6)	(14)	1,054	60	(77)	319	1,023	322
Income (loss) before income tax provision	4,140	3,243	5,924	3,555	2,928	3,287	826	(4,498)	16,862	2,543	(10,863)
Income tax provision	398	559	455	436	361	366	225	96	1,848	1,048	892
Net income (loss)	$ 3,742	$ 2,684	$ 5,469	$ 3,119	$ 2,567	$ 2,921	$ 601	$ (4,594)	$ 15,014	$ 1,495	$ (11,755)
Basic net income (loss) per share	$ 0.10	$ 0.07	$ 0.14	$ 0.08	$ 0.07	$ 0.08	$ 0.02	$ (0.12)	$ 0.38	$ 0.04	$ (0.32)
Diluted net income (loss) per share	$ 0.09	$ 0.07	$ 0.13	$ 0.08	$ 0.06	$ 0.07	$ 0.02	$ (0.12)	$ 0.37	$ 0.04	$ (0.32)