Loans - Impaired Loan (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Recorded Investment
Impaired loan, with no related allowance, recorded investment	$ 2,670	$ 1,724
Impaired loan, with related allowance, recorded investment	2,174	2,983
Impaired loan, total, recorded investment	4,844	4,707
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	2,680	1,725
Impaired loan, with related allowance, unpaid principal balance	2,174	3,026
Impaired loan, total, unpaid principal balance	4,854	4,751
Impaired loan, total, related allowance	23	35
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	2,100	2,216
Impaired loan, with related allowance, average recorded investment	2,588	2,387
Impaired loan, total, average recorded investment	4,688	4,603
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	180	1
Impaired loan, with related allowance, interest income recognized	54	65
Impaired loan, total, interest income recognized	234	66
Commercial
Recorded Investment
Impaired loan, with no related allowance, recorded investment	24	4
Impaired loan, with related allowance, recorded investment	19	91
Impaired loan, total, recorded investment	43	95
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	24	4
Impaired loan, with related allowance, unpaid principal balance	19	91
Impaired loan, total, unpaid principal balance	43	95
Impaired loan, total, related allowance	0	0
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	12	47
Impaired loan, with related allowance, average recorded investment	78	99
Impaired loan, total, average recorded investment	90	146
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	2	0
Impaired loan, with related allowance, interest income recognized	1	0
Impaired loan, total, interest income recognized	3	0
Commercial real estate | Construction and land development
Recorded Investment
Impaired loan, with no related allowance, recorded investment	158	205
Impaired loan, with related allowance, recorded investment	64	448
Impaired loan, total, recorded investment	222	653
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	157	205
Impaired loan, with related allowance, unpaid principal balance	65	449
Impaired loan, total, unpaid principal balance	222	654
Impaired loan, total, related allowance	0	6
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	198	220
Impaired loan, with related allowance, average recorded investment	272	563
Impaired loan, total, average recorded investment	470	783
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	16	0
Impaired loan, with related allowance, interest income recognized	10	26
Impaired loan, total, interest income recognized	26	26
Commercial real estate | Real estate
Recorded Investment
Impaired loan, with no related allowance, recorded investment	1,916	1,202
Impaired loan, with related allowance, recorded investment	48	390
Impaired loan, total, recorded investment	1,964	1,592
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	1,917	1,206
Impaired loan, with related allowance, unpaid principal balance	48	391
Impaired loan, total, unpaid principal balance	1,965	1,597
Impaired loan, total, related allowance	0	3
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	1,409	1,504
Impaired loan, with related allowance, average recorded investment	286	353
Impaired loan, total, average recorded investment	1,695	1,857
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	107	1
Impaired loan, with related allowance, interest income recognized	7	17
Impaired loan, total, interest income recognized	114	18
Residential | Real estate
Recorded Investment
Impaired loan, with no related allowance, recorded investment	557	127
Impaired loan, with related allowance, recorded investment	1,639	1,649
Impaired loan, total, recorded investment	2,196	1,776
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	567	124
Impaired loan, with related allowance, unpaid principal balance	1,639	1,690
Impaired loan, total, unpaid principal balance	2,206	1,814
Impaired loan, total, related allowance	22	0
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	318	126
Impaired loan, with related allowance, average recorded investment	1,593	1,034
Impaired loan, total, average recorded investment	1,911	1,160
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	38	0
Impaired loan, with related allowance, interest income recognized	32	22
Impaired loan, total, interest income recognized	70	22
Residential | Home equity
Recorded Investment
Impaired loan, with no related allowance, recorded investment	6	173
Impaired loan, with related allowance, recorded investment	386	397
Impaired loan, total, recorded investment	392	570
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	6	173
Impaired loan, with related allowance, unpaid principal balance	385	396
Impaired loan, total, unpaid principal balance	391	569
Impaired loan, total, related allowance	1	25
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	153	305
Impaired loan, with related allowance, average recorded investment	345	327
Impaired loan, total, average recorded investment	498	632
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	16	0
Impaired loan, with related allowance, interest income recognized	4	0
Impaired loan, total, interest income recognized	20	0
Consumer
Recorded Investment
Impaired loan, with no related allowance, recorded investment	9	13
Impaired loan, with related allowance, recorded investment	18	8
Impaired loan, total, recorded investment	27	21
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	9	13
Impaired loan, with related allowance, unpaid principal balance	18	9
Impaired loan, total, unpaid principal balance	27	22
Impaired loan, total, related allowance	0	1
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	10	14
Impaired loan, with related allowance, average recorded investment	14	11
Impaired loan, total, average recorded investment	24	25
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	1	0
Impaired loan, with related allowance, interest income recognized	0	0
Impaired loan, total, interest income recognized	$ 1	$ 0