Loans and Allowance for Loan Losses Schedule of Allowance for Loan Loss Activity (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Loans, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance		$ 16,518	$ 16,486	$ 16,430	$ 16,112
Allowance for loan losses, charge-offs		0	(179)	(209)	(372)
Allowance for loan losses, recoveries		555	51	702	618
Provision for loan losses	[1]	(400)	0	(250)	0
Allowance for loan losses, ending balance		16,673	16,358	16,673	16,358
Commercial [Member]
Loans, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance		3,673	3,802	3,866	3,881
Allowance for loan losses, charge-offs		0	(3)	(208)	(196)
Allowance for loan losses, recoveries		539	34	649	174
Provision for loan losses		(907)	(165)	(1,002)	(191)
Allowance for loan losses, ending balance		3,305	3,668	3,305	3,668
Construction, land and land development [Member]
Loans, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance		1,911	2,552	2,213	2,639
Allowance for loan losses, charge-offs		0	0	0	0
Allowance for loan losses, recoveries		0	0	0	398
Provision for loan losses		185	170	(117)	(315)
Allowance for loan losses, ending balance		2,096	2,722	2,096	2,722
1-4 family residential first mortgages [Member]
Loans, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance		304	350	319	317
Allowance for loan losses, charge-offs		0	0	0	0
Allowance for loan losses, recoveries		7	8	14	10
Provision for loan losses		(23)	(24)	(45)	7
Allowance for loan losses, ending balance		288	334	288	334
Home equity [Member]
Loans, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance		182	372	186	478
Allowance for loan losses, charge-offs		0	(176)	(1)	(176)
Allowance for loan losses, recoveries		6	5	17	20
Provision for loan losses		0	16	(14)	(105)
Allowance for loan losses, ending balance		188	217	188	217
Commercial real estate [Member]
Loans, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance		10,369	9,307	9,770	8,697
Allowance for loan losses, charge-offs		0	0	0	0
Allowance for loan losses, recoveries		2	3	9	9
Provision for loan losses		346	1	938	605
Allowance for loan losses, ending balance		10,717	9,311	10,717	9,311
Consumer and other [Member]
Loans, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance		79	103	76	100
Allowance for loan losses, charge-offs		0	0	0	0
Allowance for loan losses, recoveries		1	1	13	7
Provision for loan losses		(1)	2	(10)	(1)
Allowance for loan losses, ending balance		$ 79	$ 106	$ 79	$ 106

[1] The negative provisions for the various segments are related to the decline in outstanding balances in each of those portfolio segments during the time periods disclosed and/or improvement in the credit quality factors related to those portfolio segments.