Income Taxes - Carryforwards (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards
Foreign pre-tax loss	$ 0.0	$ 0.0
Federal
Operating Loss Carryforwards
Net operating loss carryforwards	611.0	611.0	$ 611.0
Net operating loss carryforwards with no expiration date		214.8
Federal | R&D credit
Operating Loss Carryforwards
Tax credit carryforwards	35.1
State
Operating Loss Carryforwards
Net operating loss carryforwards	704.8
State | R&D credit
Operating Loss Carryforwards
Tax credit carryforwards	$ 12.4
Australian Subsidiary
Operating Loss Carryforwards
Foreign Net Operating Loss written off		$ 14.9