Employee Retirement Plans - Reconciliations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Component of net periodic cost:
Effect of settlement for termination	$ 6,380
Change in plan assets:
Fair value of plan assets at beginning of year	38,053
Fair value of plan assets at end of year		$ 38,053
Amounts recognized in the consolidated balance sheets consisted
Retiree health benefit obligation	6,338	6,240
Pension plan
Component of net periodic cost:
Service cost		409	$ 356
Interest cost	1,642	1,555	1,613
Expected return on plan assets	(1,175)	(1,901)	(1,790)
Amortization of net (gain) loss	595	706	723
Effect of settlement for termination	6,380
Net periodic pension cost	7,442	769	902
Employer contributions during the period	460	7,047
Change in projected benefit obligation:
Benefit obligation at beginning of year	40,182	43,664
Actuarial (gain) loss	166	(3,296)
Benefits paid	(1,451)	(1,391)
Curtailment		(759)
Benefit obligation at end of year		40,182	43,664
Change in plan assets:
Fair value of plan assets at beginning of year	38,053	33,903
Actual return on plan assets	3,477	(1,506)
Benefits paid	(1,451)	(1,391)
Pension settlement	(40,539)
Fair value of plan assets at end of year		38,053	33,903
Funded status at end of year		(2,129)
Salaried Pension Plan
Accumulated benefit obligation	0	40,182
Pension plan | Minimum
Component of net periodic cost:
Employer contributions during the period	0
Other postretirement benefit cost
Component of net periodic cost:
Service cost	149	189	205
Interest cost	252	233	278
Amortization of net (gain) loss	(312)	(211)	(107)
Net periodic pension cost	89	211	376
Change in projected benefit obligation:
Benefit obligation at beginning of year	6,420	6,949
Participant contributions	38	25
Actuarial (gain) loss	(266)	(926)
Benefits paid	(55)	(50)
Benefit obligation at end of year	6,538	6,420	$ 6,949
Change in plan assets:
Benefits paid	$ (55)	(50)
Period of coverage under the plan	10 years
Amounts recognized in the consolidated balance sheets consisted
Accrued expenses and other current liabilities	$ 200	180
Retiree health benefit obligation	6,338	6,240
Amounts recognized in the consolidated balance sheets	$ 6,538	$ 6,420
Salaried Pension Plan
Period of service of employees	12 years