Tax credit carryforward (Details) $ in Thousands	12 Months Ended
	Mar. 31, 2016 USD ($)
Research Tax Credit Carryforward [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	$ 72,700
Research Tax Credit Carryforward [Member] | Minimum
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Mar. 31, 2022
Research Tax Credit Carryforward [Member] | Maximum
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Mar. 31, 2036
Alternative Minimum Tax [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	$ 4,300
Foreign Tax Authority [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	25,800
Tax Credit Carryforward, Valuation Allowance	$ 25,200
Foreign Tax Authority [Member] | Minimum
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Mar. 31, 2016
Foreign Tax Authority [Member] | Maximum
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Mar. 31, 2026
Foreign Tax Authority [Member] | Foreign Withholding Tax Credit [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	$ 20,000
Tax Credit Carryforward, Valuation Allowance	$ 20,000
Foreign Tax Authority [Member] | Foreign Withholding Tax Credit [Member] | Minimum
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Mar. 31, 2022
Foreign Tax Authority [Member] | Foreign Withholding Tax Credit [Member] | Maximum
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Mar. 31, 2024
State and Local Jurisdiction [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	$ 80,500
Tax Credit Carryforward, Valuation Allowance	$ 55,600
State and Local Jurisdiction [Member] | Minimum
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Mar. 31, 2016
State and Local Jurisdiction [Member] | Maximum
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Mar. 31, 2036