Defined Benefit Plan - Defined Benefit Plan (Details) - Defined Benefit Plans - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Components of net periodic benefit cost
Service cost	$ 0.8	$ 0.6	$ 1.6	$ 1.3
Interest cost	1.4	1.3	2.8	2.6
Expected return on plan assets	(2.6)	(2.6)	(5.2)	(5.1)
Amortization of unrecognized loss	1.2	0.7	2.3	1.3
Net periodic benefit cost	$ 0.8	0.0	1.5	0.1
Amortization of unrecognized loss, tax		$ (0.3)	$ (0.3)	$ (0.5)