Loans - Impaired Loan Balances By Portfolio Segment (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Recorded Investment
Impaired loan, with no related allowance, recorded investment	$ 1,751	$ 2,670
Impaired loan, with related allowance, recorded investment	1,549	2,174
Impaired loan, total, recorded investment	3,300	4,844
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	1,750	2,680
Impaired loan, with related allowance, unpaid principal balance	1,546	2,174
Impaired loan, total, unpaid principal balance	3,296	4,854
Impaired loan, total, related allowance	15	23
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	1,995	2,100
Impaired loan, with related allowance, average recorded investment	2,346	2,588
Impaired loan, total, average recorded investment	4,341	4,688
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	65	180
Impaired loan, with related allowance, interest income recognized	20	54
Impaired loan, total, interest income recognized	85	234
Commercial
Recorded Investment
Impaired loan, with no related allowance, recorded investment	18	24
Impaired loan, with related allowance, recorded investment	78	19
Impaired loan, total, recorded investment	96	43
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	17	24
Impaired loan, with related allowance, unpaid principal balance	77	19
Impaired loan, total, unpaid principal balance	94	43
Impaired loan, total, related allowance	5	0
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	17	12
Impaired loan, with related allowance, average recorded investment	78	78
Impaired loan, total, average recorded investment	95	90
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	1	2
Impaired loan, with related allowance, interest income recognized	2	1
Impaired loan, total, interest income recognized	3	3
Commercial real estate | Construction and land development
Recorded Investment
Impaired loan, with no related allowance, recorded investment	71	158
Impaired loan, with related allowance, recorded investment	61	64
Impaired loan, total, recorded investment	132	222
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	71	157
Impaired loan, with related allowance, unpaid principal balance	62	65
Impaired loan, total, unpaid principal balance	133	222
Impaired loan, total, related allowance	0	0
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	155	198
Impaired loan, with related allowance, average recorded investment	213	272
Impaired loan, total, average recorded investment	368	470
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	4	16
Impaired loan, with related allowance, interest income recognized	0	10
Impaired loan, total, interest income recognized	4	26
Commercial real estate | Real estate
Recorded Investment
Impaired loan, with no related allowance, recorded investment	1,067	1,916
Impaired loan, with related allowance, recorded investment	95	48
Impaired loan, total, recorded investment	1,162	1,964
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	1,064	1,917
Impaired loan, with related allowance, unpaid principal balance	95	48
Impaired loan, total, unpaid principal balance	1,159	1,965
Impaired loan, total, related allowance	0	0
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	1,305	1,409
Impaired loan, with related allowance, average recorded investment	224	286
Impaired loan, total, average recorded investment	1,529	1,695
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	38	107
Impaired loan, with related allowance, interest income recognized	0	7
Impaired loan, total, interest income recognized	38	114
Residential | Real estate
Recorded Investment
Impaired loan, with no related allowance, recorded investment	443	557
Impaired loan, with related allowance, recorded investment	1,086	1,639
Impaired loan, total, recorded investment	1,529	2,196
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	446	567
Impaired loan, with related allowance, unpaid principal balance	1,085	1,639
Impaired loan, total, unpaid principal balance	1,531	2,206
Impaired loan, total, related allowance	9	22
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	378	318
Impaired loan, with related allowance, average recorded investment	1,498	1,593
Impaired loan, total, average recorded investment	1,876	1,911
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	17	38
Impaired loan, with related allowance, interest income recognized	17	32
Impaired loan, total, interest income recognized	34	70
Residential | Home equity
Recorded Investment
Impaired loan, with no related allowance, recorded investment	145	6
Impaired loan, with related allowance, recorded investment	222	386
Impaired loan, total, recorded investment	367	392
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	145	6
Impaired loan, with related allowance, unpaid principal balance	220	385
Impaired loan, total, unpaid principal balance	365	391
Impaired loan, total, related allowance	1	1
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	131	153
Impaired loan, with related allowance, average recorded investment	320	345
Impaired loan, total, average recorded investment	451	498
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	5	16
Impaired loan, with related allowance, interest income recognized	1	4
Impaired loan, total, interest income recognized	6	20
Consumer
Recorded Investment
Impaired loan, with no related allowance, recorded investment	7	9
Impaired loan, with related allowance, recorded investment	7	18
Impaired loan, total, recorded investment	14	27
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	7	9
Impaired loan, with related allowance, unpaid principal balance	7	18
Impaired loan, total, unpaid principal balance	14	27
Impaired loan, total, related allowance	0	0
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	9	10
Impaired loan, with related allowance, average recorded investment	13	14
Impaired loan, total, average recorded investment	22	24
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	0	1
Impaired loan, with related allowance, interest income recognized	0	0
Impaired loan, total, interest income recognized	$ 0	$ 1