Employee Benefit Plans (Narrative) (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) employee plan	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Number of defined benefit plans | plan	4
Accumulated benefit obligations in excess of aggregate projected benefit obligation	$ 59,631,000	$ 53,865,000
Accumulated benefit obligations in excess of aggregate accumulated benefit obligation	59,631,000	53,865,000
Accumulated benefit obligations in excess of aggregate fair value of plan assets	0	0
401 (k) plan cost recognized	$ 1,933,000	$ 1,793,000	$ 1,736,000
Hourly Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Period for amortization of benefit plan gains and losses	13 years 2 months 12 days
Salaried Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Period for amortization of benefit plan gains and losses	12 years 5 months 15 days
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Number of defined benefit plans | plan	3
Ten-year rate of return	7.60%	8.30%	5.20%
Five-year rate of return	5.41%	3.19%	7.28%
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	1
Supplemental Employee Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Age requirement for participant	60 years
Required employment period	8 years
Supplemental Employee Retirement Plan | President and Chief Executive Officer
Defined Benefit Plan Disclosure [Line Items]
Additional benefit	$ 736,000
Service period credit upon termination	36 months
Postretirement Life Insurance
Defined Benefit Plan Disclosure [Line Items]
Number of retired employees | employee	389
Number of active employees | employee	101
Postretirement Medical
Defined Benefit Plan Disclosure [Line Items]
Number of retired employees | employee	126
Employee contribution percentage	100.00%