Condensed Consolidated Statements of Operations (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Net revenues	$ 41,779	$ 39,743	$ 83,277	$ 77,556
Cost of revenues	14,119	17,758	30,148	34,564
Gross profit	27,660	21,985	53,129	42,992
Operating expenses:
Research and development	24,037	22,411	51,522	44,028
Selling, general and administrative	8,342	8,373	17,041	17,137
Restructuring	0	15	0	111
Total operating expenses	32,379	30,799	68,563	61,276
Operating loss	(4,719)	(8,814)	(15,434)	(18,284)
Realized gain on short-term investments and interest income, net	242	257	472	1,876
Other income, net	15	8	32	33
Loss before taxes	(4,462)	(8,549)	(14,930)	(16,375)
Income tax expense (benefit)	178	(488)	249	(910)
Net loss	$ (4,640)	$ (8,061)	$ (15,179)	$ (15,465)
Basic and diluted net loss per share (in dollars per share)	$ (0.05)	$ (0.10)	$ (0.18)	$ (0.19)
Shares used in calculating basic and diluted net loss per share (in shares)	85,984	82,176	85,486	81,680