Income Taxes - Deferred Tax Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Deferred tax assets:
Net operating loss carryforwards	$ 294,910	$ 310,276
Research and development credit carryforwards	79,839	78,696
Inventory write-downs and other reserves	8,068	9,046
Capitalization of research and development costs	5,915	8,038
Goodwill	4,007	7,431
Intangible assets	32,290	40,201
Investment impairment	3,494	4,958
Stock-based compensation	26,664	31,177
Depreciation and amortization	3,253	165
Other	1,182	1,056
Total deferred tax assets	459,622	491,044
Valuation allowance	(459,081)	(490,629)
Total deferred tax benefit	$ 541	$ 415