Employee Benefit Plans - Postretirement Benefit Plans (Details) - Postretirement Plans - USD ($)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Estimated future benefit payments, net of subsidies:
2021	$ 6,800,000
2022	6,200,000
2023	5,600,000
2024	5,000,000.0
2025	4,600,000
Subsequent five years	17,000,000.0
Change in projected benefit obligation:
Projected benefit obligation — beginning of year	63,600,000	$ 68,800,000
Interest cost	1,600,000	2,400,000	$ 2,300,000
Actuarial losses	1,900,000	2,500,000
Benefits paid	(6,600,000)	(8,100,000)
Plan amendment	0	(1,800,000)
Other	0	(200,000)
Projected benefit obligation — end of year	60,500,000	63,600,000	68,800,000
Funded status at year-end	(60,500,000)	(63,600,000)
Other assets	0
Accrued expenses	6,700,000	7,200,000
Other long-term liabilities	53,800,000	56,400,000
Net amount recognized	(60,500,000)	(63,600,000)
Amount recognized in accumulated other comprehensive income (pre-tax) consists of — net prior service (credits) costs	(20,200,000)	(24,900,000)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	0	0	0
Interest cost	1,600,000	2,400,000	2,300,000
Amortization of unrecognized prior service credits	(4,700,000)	(4,000,000.0)	(4,000,000.0)
Recognized net actuarial (gains) losses	1,900,000	2,500,000	(2,300,000)
Total net periodic pension benefit expense	$ (1,200,000)	$ 900,000	$ (4,000,000.0)
Assumptions - Actuarial assumptions used in accounting for plans
Health care cost trend rate for next year	6.50%	6.75%	7.00%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)	5.00%	5.00%	5.00%
Year that the rate reaches the ultimate trend rate	2027	2027	2027
Discount rate used in determining net periodic postretirement benefit expense	2.97%	4.09%	3.34%
Discount rate used in determining year-end postretirement benefit obligation	2.00%	2.97%	4.09%

Amount, before tax, of accumulated other comprehensive (income) loss for cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

Name:	us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.