Loans and Allowance for Loan Losses (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Classified loans	$ 16,000		$ 25,600		$ 16,000	$ 25,600	$ 16,600
Delinquency rate	0.35%				0.35%		0.31%
Decrease in ending balance of allowance for loan losses						45.00%		48.20%
Provision (credit) for loan losses					$ 280
Charge-offs	$ 8	$ 352	3	$ 11	360
Loans Serviced for Others [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real estate loans serviced for others	108,907				108,907		$ 98,262
Agricultural Sector [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDRs loan	209				209
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Decrease in ending balance of allowance for loan losses						50.20%		47.80%
Charge-offs		224
Commercial and Industrial Sector [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase decrease in loans		2,800			$ 2,000		$ 3,200
Charge-offs		$ 110		$ 7