Loans (Composition of Total Loans Outstanding) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 819,753		$ 817,529
Less allowance for credit losses	(5,594)	$ (5,267)	(5,373)	$ (5,303)	$ (5,247)	$ (4,935)
Net loans	814,159		812,156
Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	88,249		87,581
Less allowance for credit losses	(246)	(245)	(349)	(403)	(314)	(216)
Commercial Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	461,012		465,486
Less allowance for credit losses	(2,798)	(2,634)	(2,531)	(2,472)	(2,370)	(2,375)
Commercial Term [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	120,786		123,175
Less allowance for credit losses	(648)	(625)	(709)	(793)	(891)	(989)
Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	84,428		72,755
Less allowance for credit losses	(1,106)	(1,208)	(969)	(873)	(866)	(569)
Consumer: Home Equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	59,433		62,560
Less allowance for credit losses	(186)	(189)	(196)	(202)	(191)	(195)
Consumer: Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	5,845		5,972
Less allowance for credit losses	$ (81)	$ (84)	$ (61)	$ (62)	$ (64)	$ (64)