Loans (Composition of Total Loans Outstanding) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 885,320		$ 845,897
Less allowance for credit losses	(6,188)	$ (6,145)	(5,843)	$ (5,267)	$ (5,418)	$ (5,373)
Net loans	879,132		840,054
Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	98,858		93,959
Less allowance for credit losses	(207)	(226)	(221)	(245)	(247)	(349)
Commercial Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	516,772		484,868
Less allowance for credit losses	(3,076)	(2,987)	(2,856)	(2,634)	(2,597)	(2,531)
Commercial Term [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	130,565		129,535
Less allowance for credit losses	(889)	(904)	(845)	(625)	(774)	(709)
Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	80,594		75,014
Less allowance for credit losses	(1,355)	(1,219)	(1,128)	(1,208)	(1,059)	(969)
Consumer: Home Equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	53,173		56,844
Less allowance for credit losses	(196)	(176)	(183)	(189)	(196)	(196)
Consumer: Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	5,358		5,677
Less allowance for credit losses	$ (49)	$ (55)	$ (63)	$ (84)	$ (63)	$ (61)