Income Taxes - Tax Credit Carryforwards (Details) $ in Millions	Dec. 31, 2019 USD ($)
Research and Development Tax Credit | Federal
Tax Credit Carryforwards
Tax credit carryforwards	$ 11.2
Research and Development Tax Credit | State
Tax Credit Carryforwards
Tax credit carryforwards	9.4
Orphan Drug Tax Credit | Federal
Tax Credit Carryforwards
Tax credit carryforwards	92.5
Investment Tax Credit | State
Tax Credit Carryforwards
Tax credit carryforwards	$ 0.8