Retirement Plans and Other Postretirement Benefits - Defined Benefit Plan and Supplemental Retirement Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan
Change in benefit obligation:
Projected benefit obligation at beginning of year	$ 24,820	$ 25,075	$ 28,432
Service cost	650	650	650
Interest cost	731	997	947
Plan amendments	0	0	0
Actuarial loss (gain)	1,021	101	(2,208)
Benefits paid	(1,538)	(2,003)	(2,746)
Settlements	(1,392)	0	0
Projected benefit obligation at end of year	24,292	24,820	25,075
Change in plan assets:
Fair value of plan assets at beginning of year	23,164	22,090	25,843
Actual return on plan assets	2,253	3,471	(640)
Employer contributions	0	0	0
Benefits paid	(1,538)	(2,003)	(2,746)
Expenses paid	(542)	(394)	(367)
Settlements	(1,392)	0	0
Fair value of plan assets at end of year	21,945	23,164	22,090
Funded status	(2,347)	(1,656)	(2,985)
Prepaid (accrued) benefit expense	5,485	6,690	7,425
Total amount recognized in Consolidated Balance Sheets, all in Other liabilities	(2,347)	(1,656)	(2,985)
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Prior service cost	0	0	0
Net actuarial loss	(7,833)	(8,345)	10,410
Total amount recognized in AOCI	(7,833)	(8,345)	10,410
Information for pension plans with an accumulated benefit obligation greater than plan assets:
Projected benefit obligation	24,292	24,820	25,075
Accumulated benefit obligation	24,292	24,820	25,075
Fair value of plan assets	21,945	23,164	22,090
Supplemental Defined Benefit Plans
Change in benefit obligation:
Projected benefit obligation at beginning of year	15,228	15,404	16,832
Service cost	0	0	0
Interest cost	453	620	566
Plan amendments	0	0	0
Actuarial loss (gain)	1,318	516	(789)
Benefits paid	(1,312)	(1,312)	(1,205)
Settlements	0	0	0
Projected benefit obligation at end of year	15,687	15,228	15,404
Change in plan assets:
Fair value of plan assets at beginning of year	0	0	0
Actual return on plan assets	0	0	0
Employer contributions	1,312	1,312	1,205
Benefits paid	(1,312)	(1,312)	(1,205)
Expenses paid	0	0	0
Settlements	0	0	0
Fair value of plan assets at end of year	0	0	0
Funded status	(15,687)	(15,228)	(15,404)
Prepaid (accrued) benefit expense	(9,327)	(9,884)	(10,320)
Total amount recognized in Consolidated Balance Sheets, all in Other liabilities	(15,687)	(15,228)	(15,404)
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Prior service cost	0	0	0
Net actuarial loss	(6,360)	(5,345)	5,084
Total amount recognized in AOCI	(6,360)	(5,345)	5,084
Information for pension plans with an accumulated benefit obligation greater than plan assets:
Projected benefit obligation	15,687	15,228	15,404
Accumulated benefit obligation	15,687	15,228	15,404
Fair value of plan assets	$ 0	$ 0	$ 0