Tax credit carryforward (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Mar. 31, 2015
Research Tax Credit Carryforward [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	57.4
Research Tax Credit Carryforward [Member] | Minimum [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Mar. 31, 2022
Research Tax Credit Carryforward [Member] | Maximum [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Mar. 31, 2035
Alternative Minimum Tax [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	3.7
Foreign Tax Authority [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	23.1
Tax Credit Carryforward, Valuation Allowance	23.0
Foreign Tax Authority [Member] | Minimum [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Mar. 31, 2016
Foreign Tax Authority [Member] | Maximum [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Mar. 31, 2025
State and Local Jurisdiction [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	59.1
Tax Credit Carryforward, Valuation Allowance	34.4
State and Local Jurisdiction [Member] | Minimum [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Mar. 31, 2016
State and Local Jurisdiction [Member] | Maximum [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Mar. 31, 2035