Employee Benefit Plans - Reconciliation of the Fair Values Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3) from the Beginning of the Year to the End of the Year (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of fair value measurements of plan assets using significant observable inputs
Fair value of plan assets, beginning of year	$ 150.4
Fair value of plan assets, end of year	161.3	$ 150.4
Insurance Group Annuity Contracts
Reconciliation of fair value measurements of plan assets using significant observable inputs
Fair value of plan assets, beginning of year	14.5
Fair value of plan assets, end of year	14.4	14.5
Level 3
Reconciliation of fair value measurements of plan assets using significant observable inputs
Fair value of plan assets, beginning of year	14.5
Fair value of plan assets, end of year	14.4	14.5
Level 3 | Insurance Group Annuity Contracts
Reconciliation of fair value measurements of plan assets using significant observable inputs
Fair value of plan assets, beginning of year	14.5	106.5
Distribution of MFS		(89.9)
Actual return on plan assets		2.0
Benefits paid	(1.5)	(1.4)
Currency translation adjustment	1.3	(2.7)
Fair value of plan assets, end of year	$ 14.4	$ 14.5