Employee Benefit Plans (Narrative) (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) plan employee	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Number of defined benefit plans | plan	4
401 (k) plan cost recognized	$ 1,834,000	$ 1,933,000	$ 1,793,000
Hourly Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Period for amortization of benefit plan gains and losses	12 years 7 months 20 days
Salaried Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Period for amortization of benefit plan gains and losses	11 years 10 months 24 days
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Number of defined benefit plans | plan	4
2021	$ 6,938,000
2022	6,516,000
2023	6,123,000
2024	5,744,000
2025	60,349,000
2026 - 2030	$ 28,378,000
Ten-year rate of return	6.91%	7.59%	8.26%
Five-year rate of return	7.51%	5.41%	3.19%
Pension Benefits | Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Number of defined benefit plans | plan	2
Pension Benefits | Nonqualified Plan
Defined Benefit Plan Disclosure [Line Items]
Number of defined benefit plans | plan	2
Supplemental Employee Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Age requirement for participant	60 years
Required employment period	8 years
2021	$ 0
2022	0
2023	0
2024	0
2025	54,992,000
2026 - 2030	6,866,000
Supplemental Employee Retirement Plan | President and Chief Executive Officer
Defined Benefit Plan Disclosure [Line Items]
Additional benefit	$ 1,788,000
Service period credit upon termination	36 months
Postretirement Life Insurance
Defined Benefit Plan Disclosure [Line Items]
Number of retired employees | employee	365
Number of active employees | employee	97
Postretirement Medical
Defined Benefit Plan Disclosure [Line Items]
2021	$ 624,000
2022	623,000
2023	623,000
2024	616,000
2025	602,000
2026 - 2030	$ 2,698,000
Employee contribution percentage	100.00%
Number of retired employees | employee	97