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, 2016	Dec. 31, 2015	Dec. 31, 2014
Assumptions (end of period):
Discount rate used in determining benefit obligation	3.88%	4.12%	3.86%
Reconciliation of funded status (end of period):
Accumulated benefit obligation	$ (12,618)	$ (12,915)	$ (13,909)
Projected benefit obligation	(12,618)	(12,915)	(13,909)
Fair value of plan assets	10,415	10,419	11,290
Defined benefit plan, funded status of plan, total	(2,203)	(2,496)	(2,619)
Net actuarial loss	(4,102)	(3,957)	(4,000)
Accumulated other comprehensive loss	(4,102)	(3,957)	(4,000)
Prepaid pension cost	1,899	1,461	1,381
Net amount recognized as of December 31	(2,203)	(2,496)	(2,619)
Changes in projected benefit obligation:
Benefit obligation as of beginning of period	12,915	13,909	12,284
Interest cost	512	518	532
Actuarial liability loss	19	(646)	1,947
Benefits paid	(828)	(866)	(854)
Benefit obligation as of end of period	12,618	12,915	13,909
Change in plan assets:
Fair value of plan assets as of beginning of period	10,419	11,290	10,851
Actual return on plan assets (net of expenses)	415	(5)	760
Employer contributions	409		533
Benefits paid	828	866	854
Fair value of plan assets as of end of period	10,415	10,419	11,290
Net periodic pension cost:
Service cost - benefits earned during the period
Interest cost on projected benefit obligation	512	518	532
Expected return on plan assets	(653)	(701)	(698)
Recognized actuarial loss	112	103	162
Net periodic pension cost	$ (29)	$ (80)	$ (4)
Discount rate	4.12%	3.86%	4.49%
Expected return on plan assets	6.50%	6.50%	6.50%