Income Taxes - Deferred Tax Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Mar. 31, 2012
Deferred tax assets:
Net operating loss carryforwards	$ 310,276	$ 284,210
Research and development credit carryforwards	78,696	78,621
Inventory write-downs and other reserves	9,046	9,748
Capitalization of research and development costs	8,038	8,451
Goodwill	7,431	8,248
Intangible assets	40,201	46,681
Investment impairment	4,958	4,083
Stock-based compensation	31,177	26,975
Depreciation and amortization	165	0
Other	1,056	979
Total deferred tax assets	491,044	467,996
Deferred tax liabilities:
Depreciation and amortization	0	(2,402)
Intangible assets	0	0
Net deferred tax asset	491,044	465,594
Valuation allowance	(490,629)	(465,281)
Total deferred tax benefit	$ 415	$ 313