Income Taxes - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Operating Loss Carryforwards [Line Items]
Tax expense as result of remeasurment of deferred tax asset due to Tax Cuts and Jobs Act	$ 3.4
Research And Development Tax Credit
Operating Loss Carryforwards [Line Items]
Adjustment to income tax credit, reduction in income tax expense	$ 5.5