Retirement Plans (Changes in Benefit Obligations, Components of Benefit Costs, Weighted-Average Assumptions, and Plan Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Assumptions (end of period):
Discount rate used in determining benefit obligation	2.12%	2.98%
Reconciliation of funded status (end of period):
Accumulated benefit obligation	$ (13,252)	$ (12,376)
Projected benefit obligation	(13,252)	(12,376)
Fair value of plan assets	11,393	10,988
Funded status	(1,859)	(1,388)
Net actuarial loss	(4,672)	(4,010)
Accumulated other comprehensive loss	(4,672)	(4,010)
Prepaid pension cost	2,813	2,622
Net amount recognized as of December 31	(1,859)	(1,388)
Changes in projected benefit obligation:
Benefit obligation as of beginning of period	12,376	11,687
Interest cost	355	454
Actuarial liability loss	1,352	1,083
Benefits paid	(831)	(848)
Benefit obligation as of end of period	13,252	12,376	$ 11,687
Change in plan assets:
Fair value of plan assets as of beginning of period	10,988	9,669
Actual return on plan assets (net of expenses)	1,236	1,667
Employer contributions	0	500
Benefits Paid	(831)	(848)
Fair value of plan assets as of end of period	11,393	10,988	9,669
Net periodic pension cost:
Service cost - benefits earned during the period
Interest cost	355	454
Expected return on plan assets	(684)	(607)
Recognized actuarial loss	138	143
Net periodic pension cost	$ (191)	$ (10)
Discount rate	2.98%	4.05%
Expected return on plan assets	6.50%	6.50%