Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Tax Credit Carryforward [Line Items]
Decrease in deferred tax asset due to Tax Act	$ 30.5
Increase in valuation allowance	(6.8)	$ 18.9
Net operating loss carryforwards	190.3	152.5
Unrecognized excess tax benefits	1.2	1.2
Research Tax Credit Carryforward
Tax Credit Carryforward [Line Items]
Research and development tax credit carryforwards	$ 13.4	$ 5.6