Borrowed Funds (Summary of Short Term Borrowings) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Short-term Debt [Line Items]
Outstanding at end of year	$ 48,845	$ 36,000
Weighted average interest rate at year end	0.15%	0.16%
Maximum amount outstanding as of any month end	$ 58,438	$ 39,456
Average amount outstanding	$ 37,326	$ 30,899
Securities Sold under Agreements to Repurchase [Member]
Short-term Debt [Line Items]
Approximate weighted average rate during the period	0.19%	0.19%