Income Taxes - Operating Loss Carryforwards (Details) - USD ($) $ in Millions	Mar. 31, 2019	Mar. 31, 2018
Operating Loss Carryforwards [Line Items]
Capital loss carryforward	$ 9.6	$ 10.6
Refundable foreign tax credits	18.5
Tax credits, research activity	129.3
Tax credits, prior year	4.5
Tax credits, foreign jurisdictions	45.8
Foreign Tax Authority and Federal and State Jurisdiction
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	94.3
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Tax credit carryforward, amount	158.5
Foreign Withholding Tax Credit | Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Tax credit carryforward, amount	$ 19.9