Retirement Plans - Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
United States
Defined Benefit Plan, Pension Plan with Accumulated Benefit Obligation in Excess of Plan Assets [Abstract]
Projected benefit obligation, end of year	$ 63.7	$ 64.9
Accumulated benefit obligation, end of year	63.7	64.9
Plan assets at fair value, end of year	48.8	49.8
Germany
Defined Benefit Plan, Pension Plan with Accumulated Benefit Obligation in Excess of Plan Assets [Abstract]
Projected benefit obligation, end of year	26.8	24.1
Accumulated benefit obligation, end of year	26.8	24.1
Plan assets at fair value, end of year	$ 17.5	$ 15.2