Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Mar. 31, 2015
Deferred tax assets:
Net operating loss carryforwards	$ 356,106	$ 315,773
Research and development credit carryforwards	84,259	81,546
Inventory write-downs and other reserves	7,656	7,642
Capitalization of research and development costs	7,348	6,245
Goodwill	2,207	3,147
Intangible assets	19,142	26,031
Investment impairment	3,583	3,982
Stock-based compensation	5,188	28,921
Depreciation and amortization	2,548	1,903
Other	1,174	970
Total deferred tax assets	489,211	476,160
Valuation allowance	(488,646)	(475,545)
Net deferred tax asset	$ 565	$ 615