Retirement Plans and Other Postretirement Benefits - Defined Benefit Plan and Supplemental Retirement Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan
Change in benefit obligation:
Projected benefit obligation at beginning of year	$ 25,075	$ 28,432	$ 29,407
Service cost	650	650	650
Interest cost	997	947	1,091
Plan amendments	0	0	0
Actuarial loss (gain)	101	(2,208)	(721)
Benefits paid	(2,003)	(2,746)	(1,995)
Settlements	0	0	0
Projected benefit obligation at end of year	24,820	25,075	28,432
Change in plan assets:
Fair value of plan assets at beginning of year	22,090	25,843	25,446
Actual return on plan assets	3,471	(640)	2,909
Employer contributions	0	0	0
Benefits paid	(2,003)	(2,746)	(1,995)
Expenses paid	(394)	(367)	(517)
Settlements	0	0	0
Fair value of plan assets at end of year	23,164	22,090	25,843
Funded status	(1,656)	(2,985)	(2,589)
Prepaid (accrued) benefit expense	6,690	7,425	8,016
Total amount recognized in Consolidated Balance Sheets, all in Other liabilities	(1,656)	(2,985)	(2,589)
Amounts recognized in accumulated other comprehensive income (loss) (AOCI):
Prior service cost	0	0	0
Net actuarial loss	(8,345)	10,410	10,605
Total amount recognized in AOCI	(8,345)	10,410	10,605
Information for pension plans with an accumulated benefit obligation greater than plan assets:
Projected benefit obligation	24,820	25,075	28,432
Accumulated benefit obligation	24,820	25,075	28,432
Fair value of plan assets	23,164	22,090	25,843
Supplemental Defined Benefit Plans
Change in benefit obligation:
Projected benefit obligation at beginning of year	15,404	16,832	16,847
Service cost	0	0	0
Interest cost	620	566	631
Plan amendments	0	0	0
Actuarial loss (gain)	516	(789)	805
Benefits paid	(1,312)	(1,205)	(1,451)
Settlements	0	0	0
Projected benefit obligation at end of year	15,228	15,404	16,832
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	1,205	1,451
Benefits paid	(1,312)	(1,205)	(1,451)
Expenses paid	0	0	0
Settlements	0	0	0
Fair value of plan assets at end of year	0	0	0
Funded status	(15,228)	(15,404)	(16,832)
Prepaid (accrued) benefit expense	(9,884)	(10,320)	(10,648)
Total amount recognized in Consolidated Balance Sheets, all in Other liabilities	(15,228)	(15,404)	(16,832)
Amounts recognized in accumulated other comprehensive income (loss) (AOCI):
Prior service cost	0	0	0
Net actuarial loss	(5,345)	5,084	6,184
Total amount recognized in AOCI	(5,345)	5,084	6,184
Information for pension plans with an accumulated benefit obligation greater than plan assets:
Projected benefit obligation	15,228	15,404	16,832
Accumulated benefit obligation	15,228	15,404	16,832
Fair value of plan assets	$ 0	$ 0	$ 0