Pension and Postretirement Benefit Plans - Components of Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SERP I and SERP II
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 0	$ 0
Interest cost	140	179	160
Amortization of prior service cost	0	0	0
Recognition of net actuarial loss	94	62	70
Net periodic pension cost	$ 234	$ 241	$ 230
Discount Rate Used in the Calculation of Periodic Pension Costs	2.80%	3.95%	3.30%
PRBP
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 0	$ 0
Interest cost	5	8	9
Amortization of prior service cost	0	0	0
Recognition of net actuarial loss	24	17	30
Net periodic pension cost	$ 29	$ 25	$ 39
Discount Rate Used in the Calculation of Periodic Pension Costs	2.20%	3.45%	2.75%