Retirement Plans and Other Postretirement Benefits - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) plan	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2006 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Number of supplemental defined benefit plans frozen | plan	2
Pension cost (credit)	$ 10.0	$ 9.3	$ 8.9
Health reimbursement account, amount	1.3			$ 7.3
Health reimbursement accounts funding	$ 0.1	$ 0.1	$ 0.1
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plan to approximate allocation	35.00%
Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plan to approximate allocation	65.00%
Defined Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Expected amortization of gain (loss) next year	$ 0.5
Supplemental Defined Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Expected amortization of gain (loss) next year	$ 0.4
Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Number of retirement plans | plan	2
Qualified Plan | 401(k) plan | Defined Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Frozen supplemental defined benefit plans, vesting percentage	100.00%
Employer matching contribution as percent of employees' gross pay	3.00%
Percentage of employer match	5.00%
Vesting period for Company contributions	5 years
Nonqualified Plan
Defined Benefit Plan Disclosure [Line Items]
Number of retirement plans | plan	3