Loans (Composition of Total Loans Outstanding) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 908,293		$ 845,897
Less allowance for credit losses	(6,559)	$ (6,188)	(5,843)	$ (5,594)	$ (5,267)	$ (5,373)
Net loans	901,734		840,054
Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	103,093		93,959
Less allowance for credit losses	(163)	(207)	(221)	(246)	(245)	(349)
Commercial Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	524,672		484,868
Less allowance for credit losses	(3,289)	(3,076)	(2,856)	(2,798)	(2,634)	(2,531)
Commercial Term [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	140,810		129,535
Less allowance for credit losses	(987)	(889)	(845)	(648)	(625)	(709)
Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	81,297		75,014
Less allowance for credit losses	(1,068)	(1,355)	(1,128)	(1,106)	(1,208)	(969)
Consumer: Home Equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	53,210		56,844
Less allowance for credit losses	(196)	(196)	(183)	(186)	(189)	(196)
Consumer: Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	5,211		5,677
Less allowance for credit losses	$ (48)	$ (49)	$ (63)	$ (81)	$ (84)	$ (61)