Retirement Plans - Allocation of Plan Assets, Pension Plan (Details) - Pension Plan - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	$ 228.9	$ 256.4	$ 235.8
Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	1.2	66.7
Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	9.8	90.9
Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	1.5	7.0
Cash and Cash Equivalents | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	1.2	3.2
Cash and Cash Equivalents | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	0.3	3.8
Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets		63.5
Equity | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets		63.5
Equity | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets		0.0
Real Estate Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	9.5
Real Estate Funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	0.0
Real Estate Funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	9.5
Assets Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	217.9	98.8
Assets Measured at NAV | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	0.0	0.0
Assets Measured at NAV | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	$ 0.0	0.0
Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets		87.1
Fixed Income | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets		0.0
Fixed Income | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets		$ 87.1