Loans - Impaired Loan Balances By Portfolio Segment (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Recorded Investment
Impaired loan, with no related allowance, recorded investment	$ 1,304	$ 1,099
Impaired loan, with related allowance, recorded investment	311	235
Impaired loan, total, recorded investment	1,615	1,334
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	1,304	1,096
Impaired loan, with related allowance, unpaid principal balance	306	231
Impaired loan, total, unpaid principal balance	1,610	1,327
Impaired loan, total, related allowance	74	64
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	1,121	1,571
Impaired loan, with related allowance, average recorded investment	273	863
Impaired loan, total, average recorded investment	1,394	2,434
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	65	89
Impaired loan, with related allowance, interest income recognized	15	50
Impaired loan, total, interest income recognized	80	139
Commercial
Recorded Investment
Impaired loan, with no related allowance, recorded investment	0	28
Impaired loan, with related allowance, recorded investment	52	62
Impaired loan, total, recorded investment	52	90
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	0	28
Impaired loan, with related allowance, unpaid principal balance	47	58
Impaired loan, total, unpaid principal balance	47	86
Impaired loan, total, related allowance	47	55
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	8	44
Impaired loan, with related allowance, average recorded investment	55	354
Impaired loan, total, average recorded investment	63	398
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	0	14
Impaired loan, with related allowance, interest income recognized	2	40
Impaired loan, total, interest income recognized	2	54
Commercial real estate | Construction and land development
Recorded Investment
Impaired loan, with no related allowance, recorded investment	0	0
Impaired loan, with related allowance, recorded investment	0	0
Impaired loan, total, recorded investment	0	0
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	0	0
Impaired loan, with related allowance, unpaid principal balance	0	0
Impaired loan, total, unpaid principal balance	0	0
Impaired loan, total, related allowance	0	0
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	0	0
Impaired loan, with related allowance, average recorded investment	0	21
Impaired loan, total, average recorded investment	0	21
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	0	0
Impaired loan, with related allowance, interest income recognized	0	0
Impaired loan, total, interest income recognized	0	0
Commercial real estate | Real estate
Recorded Investment
Impaired loan, with no related allowance, recorded investment	530	376
Impaired loan, with related allowance, recorded investment	0	0
Impaired loan, total, recorded investment	530	376
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	527	373
Impaired loan, with related allowance, unpaid principal balance	0	0
Impaired loan, total, unpaid principal balance	527	373
Impaired loan, total, related allowance	0	0
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	404	542
Impaired loan, with related allowance, average recorded investment	0	18
Impaired loan, total, average recorded investment	404	560
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	29	36
Impaired loan, with related allowance, interest income recognized	0	0
Impaired loan, total, interest income recognized	29	36
Residential | Real estate
Recorded Investment
Impaired loan, with no related allowance, recorded investment	731	646
Impaired loan, with related allowance, recorded investment	259	173
Impaired loan, total, recorded investment	990	819
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	734	646
Impaired loan, with related allowance, unpaid principal balance	259	173
Impaired loan, total, unpaid principal balance	993	819
Impaired loan, total, related allowance	27	9
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	663	875
Impaired loan, with related allowance, average recorded investment	218	342
Impaired loan, total, average recorded investment	881	1,217
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	32	29
Impaired loan, with related allowance, interest income recognized	13	9
Impaired loan, total, interest income recognized	45	38
Residential | Home equity
Recorded Investment
Impaired loan, with no related allowance, recorded investment	43	49
Impaired loan, with related allowance, recorded investment	0	0
Impaired loan, total, recorded investment	43	49
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	43	49
Impaired loan, with related allowance, unpaid principal balance	0	0
Impaired loan, total, unpaid principal balance	43	49
Impaired loan, total, related allowance	0	0
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	46	108
Impaired loan, with related allowance, average recorded investment	0	128
Impaired loan, total, average recorded investment	46	236
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	4	10
Impaired loan, with related allowance, interest income recognized	0	1
Impaired loan, total, interest income recognized	4	11
Consumer
Recorded Investment
Impaired loan, with no related allowance, recorded investment	0	0
Impaired loan, with related allowance, recorded investment	0	0
Impaired loan, total, recorded investment	0	0
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	0	0
Impaired loan, with related allowance, unpaid principal balance	0	0
Impaired loan, total, unpaid principal balance	0	0
Impaired loan, total, related allowance	0	0
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	0	2
Impaired loan, with related allowance, average recorded investment	0	0
Impaired loan, total, average recorded investment	0	2
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	0	0
Impaired loan, with related allowance, interest income recognized	0	0
Impaired loan, total, interest income recognized	$ 0	$ 0