Defined Benefit Plan - Defined Benefit Plan (Details) - Defined Benefit Plans - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Components of net periodic benefit cost
Service cost	$ 0.8	$ 0.7
Interest cost	1.4	1.3
Expected return on plan assets	(2.6)	(2.5)
Amortization of unrecognized loss	1.1	0.6
Net periodic benefit cost	0.7	0.1
Amortization of unrecognized loss, tax	$ (0.3)	$ (0.2)