Pension Plans and Other Postretirement Benefits - Defined Benefit Plan and Supplemental Retirement Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan
Change in benefit obligation:
Benefit obligations at beginning of year	$ 28,432	$ 29,407	$ 31,233
Service cost	650	650	650
Interest cost	947	1,091	1,244
Plan amendments	0	0	0
Actuarial loss (gain)	2,208	721	220
Benefits paid	(2,746)	(1,995)	(3,500)
Settlements	0	0	0
Benefit obligations at beginning of year	25,075	28,432	29,407
Change in plan assets:
Fair value of plan assets at beginning of year	25,843	25,446	27,667
Actual return on plan assets	(640)	2,909	1,766
Employer contributions	0	0	0
Benefits paid	(2,746)	(1,995)	(3,500)
Expenses paid	(367)	(517)	(487)
Settlements	0	0	0
Fair value of plan assets at end of year	22,090	25,843	25,446
Funded status	2,985	2,589	3,961
Prepaid (accrued) benefit expense	7,425	8,016	8,653
Total amount recognized in Consolidated Balance Sheets, all in Other liabilities	(2,985)	(2,589)	(3,961)
Amounts recognized in accumulated other comprehensive income (loss) ("AOCI"):
Prior service cost	0	0	0
Net actuarial loss	10,410	10,605	12,613
Total amount recognized in AOCI	10,410	10,605	12,613
Information for pension plans with an accumulated benefit obligation greater than plan assets:
Projected benefit obligation	25,075	28,432	29,407
Accumulated benefit obligation	25,075	28,432	29,407
Fair value of plan assets	22,090	25,843	25,446
Supplemental Defined Benefit Plans
Change in benefit obligation:
Benefit obligations at beginning of year	16,832	16,847	17,004
Service cost	0	0	0
Interest cost	566	631	687
Plan amendments	0	0	0
Actuarial loss (gain)	789	(805)	(488)
Benefits paid	(1,205)	(1,451)	(1,332)
Settlements	0	0	0
Benefit obligations at beginning of year	15,404	16,832	16,847
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	1,205	1,451	1,332
Benefits paid	(1,205)	(1,451)	(1,332)
Expenses paid	0	0	0
Settlements	0	0	0
Fair value of plan assets at end of year	0	0	0
Funded status	15,404	16,832	16,847
Prepaid (accrued) benefit expense	(10,320)	(10,648)	(11,210)
Total amount recognized in Consolidated Balance Sheets, all in Other liabilities	(15,404)	(16,832)	(16,847)
Amounts recognized in accumulated other comprehensive income (loss) ("AOCI"):
Prior service cost	0	0	0
Net actuarial loss	5,084	6,184	5,637
Total amount recognized in AOCI	5,084	6,184	5,637
Information for pension plans with an accumulated benefit obligation greater than plan assets:
Projected benefit obligation	15,404	16,832	16,847
Accumulated benefit obligation	15,404	16,832	16,847
Fair value of plan assets	$ 0	$ 0	$ 0