Defined Benefit Plan - Defined Benefit Plan (Details) - Defined Benefit Plans - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Components of net periodic benefit cost
Service cost	$ 0.8	$ 0.7	$ 2.4	$ 2.0
Interest cost	1.3	1.3	4.1	3.9
Expected return on plan assets	(2.5)	(2.5)	(7.7)	(7.6)
Amortization of unrecognized loss	1.1	0.6	3.4	1.9
Net periodic benefit cost	0.7	0.1	2.2	0.2
Amortization of unrecognized loss, tax	$ 0.6	$ (0.3)	$ (0.9)	$ (0.8)