Components of deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Mar. 31, 2016
Components of Deferred Tax Assets [Abstract]
Deferred income on shipments to distributors	$ 55,674	$ 34,830
Inventory valuation	14,608	12,082
Net operating loss carryforward	91,606	63,209
Capital loss carryforward	12,927	5,707
Share-based compensation	42,547	31,410
Income tax credits	243,049	100,294
Property, plant and equipment	59,700	16,262
Accrued expenses and other	110,347	37,292
Gross deferred tax assets	630,458	301,086
Valuation allowances	(210,120)	(161,834)
Deferred tax assets, net of valuation allowances	420,338	139,252
Components of Deferred Tax Liabilities [Abstract]
Convertible debt	(606,674)	(496,626)
Intangible assets	(147,543)	(20,597)
Other	(6,296)	(6,416)
Deferred Tax Liabilities, Gross	(760,513)	(523,639)
Net deferred tax liability	(340,175)	(384,387)
Non-current deferred tax assets	68,870	14,831
Non-current deferred tax liability	$ (409,045)	$ (399,218)