Income Taxes - Carryforwards (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards
Foreign pre-tax loss	$ 3.0	$ 8.2
Federal
Operating Loss Carryforwards
Net operating loss carryforwards	636.8
Net operating loss carryforwards with no expiration date	75.0
Federal | R&D credit
Operating Loss Carryforwards
Tax credit carryforwards	31.0
State
Operating Loss Carryforwards
Net operating loss carryforwards	532.4
State | R&D credit
Operating Loss Carryforwards
Tax credit carryforwards	$ 11.1