Lease Commitments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Leases [Abstract]
Rental expense under operating leases	$ 11.5	$ 9.5	$ 11.1
Future minimum lease payments for non-cancelable operating leases
Operating Leases, Future Minimum Payments Due, Next Twelve Months	9.2
Operating Leases, Future Minimum Payments, Due in Two Years	7.1
Operating Leases, Future Minimum Payments, Due in Three Years	5.6
Operating Leases, Future Minimum Payments, Due in Four Years	4.1
Operating Leases, Future Minimum Payments, Due in Five Years	3.8
Operating Leases, Future Minimum Payments, Due Thereafter	10.8
Operating Leases, Future Minimum Payments Due	$ 40.6