Retirement Plans - Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Pension plan
Other changes in plan assets and benefit obligations recognized in other comprehensive income:
Net loss (gain)	$ 282	$ (60)
Recognition of net actuarial gain or (loss)	(67)	(75)
Total changes	215	(135)
Changes, net of taxes	155	(97)
SERP liability adjustments
Other changes in plan assets and benefit obligations recognized in other comprehensive income:
Net loss (gain)	708	486
Recognition of net actuarial gain or (loss)	(86)	(62)
Total changes	622	424
Changes, net of taxes	$ 448	$ 305

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Amount, before tax, after reclassification adjustment, of (increase) decrease in accumulated other comprehensive income for defined benefit plan.

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