Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Income Statement [Abstract]
Net revenues	$ 165,011us-gaap_SalesRevenueNet	$ 216,150us-gaap_SalesRevenueNet	$ 195,642us-gaap_SalesRevenueNet
Cost of revenues	69,297us-gaap_CostOfRevenue	85,189us-gaap_CostOfRevenue	83,048us-gaap_CostOfRevenue
Gross profit	95,714us-gaap_GrossProfit	130,961us-gaap_GrossProfit	112,594us-gaap_GrossProfit
Operating expenses:
Research and development	107,220us-gaap_ResearchAndDevelopmentExpense	146,579us-gaap_ResearchAndDevelopmentExpense	187,419us-gaap_ResearchAndDevelopmentExpense
Selling, general and administrative	33,643	38,927	51,684
Gain on sale of TPack	0	(19,699)	0
Gain on sale of building	0	(25,815)	0
Amortization of purchased intangible assets	104us-gaap_AdjustmentForAmortization	316us-gaap_AdjustmentForAmortization	1,926us-gaap_AdjustmentForAmortization
Restructuring charges	5,421us-gaap_RestructuringCharges	1,134us-gaap_RestructuringCharges	6,435us-gaap_RestructuringCharges
Total operating expenses	146,388us-gaap_OperatingExpenses	141,442us-gaap_OperatingExpenses	247,464us-gaap_OperatingExpenses
Operating loss	(50,674)us-gaap_OperatingIncomeLoss	(10,481)us-gaap_OperatingIncomeLoss	(134,870)us-gaap_OperatingIncomeLoss
Net realized gain on short-term investments and interest income, net	2,764us-gaap_InvestmentIncomeNonoperating	5,052us-gaap_InvestmentIncomeNonoperating	2,595us-gaap_InvestmentIncomeNonoperating
Other (expense) income, net	(3,056)us-gaap_OtherNonoperatingIncomeExpense	354us-gaap_OtherNonoperatingIncomeExpense	(2,394)us-gaap_OtherNonoperatingIncomeExpense
Loss before income taxes	(50,966)	(5,075)	(134,669)
Income tax expense (benefit)	1,092us-gaap_IncomeTaxExpenseBenefit	619us-gaap_IncomeTaxExpenseBenefit	(554)us-gaap_IncomeTaxExpenseBenefit
Net loss	$ (52,058)us-gaap_NetIncomeLoss	$ (5,694)us-gaap_NetIncomeLoss	$ (134,115)us-gaap_NetIncomeLoss
Basic and diluted net loss per share (in dollars per share)	$ (0.66)us-gaap_EarningsPerShareBasicAndDiluted	$ (0.08)us-gaap_EarningsPerShareBasicAndDiluted	$ (2.06)us-gaap_EarningsPerShareBasicAndDiluted
Shares used in calculating basic and diluted net loss per share	78,814	72,897	65,258

The aggregate amount of recurring noncash expense charged against earnings in the period to allocate the cost of assets over their estimated remaining economic lives.

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