Income Taxes - NOL and Tax credit carryforwards (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
State
NOL and Tax credit carryfowards
Net operating loss carryforwards	$ 120.5	$ 141.3
State | Research Tax Credit Carryforward
NOL and Tax credit carryfowards
Tax credit carryforwards	8.4	8.2
Foreign
NOL and Tax credit carryfowards
Tax credit carryforwards	55.2	55.0
Domestic | General Business Tax Credit Carryforward
NOL and Tax credit carryfowards
Tax credit carryforwards	$ 19.3	$ 16.9