Employee Benefit Plans - Fair Value of Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Total pension assets	$ 115.5	$ 99.3	$ 104.5
Level 1
Defined Benefit Plan Disclosure [Line Items]
Total pension assets	34.2	28.4
Level 2
Defined Benefit Plan Disclosure [Line Items]
Total pension assets	77.1	60.0
Level 3
Defined Benefit Plan Disclosure [Line Items]
Total pension assets	4.2	10.9	$ 12.9
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Total pension assets	56.1	50.1
Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total pension assets	31.4	26.2
Equity securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total pension assets	24.7	23.9
Global return fund
Defined Benefit Plan Disclosure [Line Items]
Total pension assets	14.6	15.7
Global return fund | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total pension assets	14.6	15.7
Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Total pension assets	13.9	11.4
Corporate bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total pension assets	13.9	11.4
Government bonds
Defined Benefit Plan Disclosure [Line Items]
Total pension assets	10.6	9.0
Government bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total pension assets	10.6	9.0
Real estate
Defined Benefit Plan Disclosure [Line Items]
Total pension assets	4.2	10.9
Real estate | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total pension assets	0.0
Real estate | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total pension assets	4.2	10.9
LDI (Liability Driven Investment)
Defined Benefit Plan Disclosure [Line Items]
Total pension assets	13.3
LDI (Liability Driven Investment) | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total pension assets	13.3
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total pension assets	2.8	2.2
Cash and cash equivalents | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total pension assets	$ 2.8	$ 2.2