Restructuring Expenses (Details) $ in Millions		9 Months Ended
	Feb. 15, 2017 Employee	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Restructuring Cost and Reserve [Line Items]
Facility-related costs incurred		$ 3.0
Number of positions eliminated | Employee	100
Restructuring expenses paid		$ 3.0
Employee severance
Restructuring Cost and Reserve [Line Items]
Accrued restructuring expenses			$ 3.8
Restructuring expenses paid			3.2
Facility-related cost
Restructuring Cost and Reserve [Line Items]
Facility-related costs incurred			0.6
Restructuring expenses paid			$ 0.2