Employee Benefit Plans - Schedule of Changes in Projected Benefit Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Amounts recognized in the consolidated balance sheets consist of:
Prepaid pension cost	$ 7,414	$ 5,758
Pension Plans
Change in projected benefit obligation:
Projected benefit obligation at beginning of period	157,743	148,479
Service cost	395	357
Interest cost	4,019	5,233
Benefit payments	(11,970)	(12,380)
Actuarial loss (gain)	14,502	16,054
Plan amendment resulting from change in collective bargaining agreement	(306)	0
Projected benefit obligation at end of period	164,383	157,743
Change in plan assets:
Fair value of plan assets at beginning of period	158,002	145,065
Actual return on assets	19,618	24,933
Employer contributions	384	384
Benefit payments	(11,970)	(12,380)
Fair value of plan assets at end of period	166,034	158,002
Funded status - net asset (liability)	1,651	259
Amounts recognized in the consolidated balance sheets consist of:
Prepaid pension cost	7,414	5,758
Accrued liabilities	(390)	(390)
Postretirement benefit obligations	(5,373)	(5,109)
Net amount recognized	1,651	259
Pre-tax components of accumulated other comprehensive loss:
Unrecognized prior service cost	204	298
Unrecognized actuarial gain	9,868	8,568
Total	10,072	8,866
Accumulated benefit obligation	164,347	157,698
Other Postretirement Benefit Plan
Change in projected benefit obligation:
Projected benefit obligation at beginning of period	1,760	1,627
Service cost	52	67
Interest cost	40	56
Benefit payments	(38)	(22)
Actuarial loss (gain)	100	32
Projected benefit obligation at end of period	1,914	1,760
Change in plan assets:
Funded status - net asset (liability)	(1,914)	(1,760)
Amounts recognized in the consolidated balance sheets consist of:
Accrued liabilities	(270)	(160)
Postretirement benefit obligations	(1,644)	(1,600)
Net amount recognized	(1,914)	(1,760)
Pre-tax components of accumulated other comprehensive loss:
Unrecognized prior service cost	(13)	(15)
Unrecognized actuarial gain	599	548
Total	$ 586	$ 533