Loans - Impaired Loan Balances By Portfolio Segment (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Recorded Investment
Impaired loan, with no related allowance, recorded investment	$ 1,043	$ 1,099
Impaired loan, with related allowance, recorded investment	230	235
Impaired loan, total, recorded investment	1,273	1,334
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	1,041	1,096
Impaired loan, with related allowance, unpaid principal balance	226	231
Impaired loan, total, unpaid principal balance	1,267	1,327
Impaired loan, total, related allowance	62	64
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	1,071	1,571
Impaired loan, with related allowance, average recorded investment	233	863
Impaired loan, total, average recorded investment	1,304	2,434
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	16	89
Impaired loan, with related allowance, interest income recognized	3	50
Impaired loan, total, interest income recognized	19	139
Commercial
Recorded Investment
Impaired loan, with no related allowance, recorded investment	0	28
Impaired loan, with related allowance, recorded investment	59	62
Impaired loan, total, recorded investment	59	90
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	0	28
Impaired loan, with related allowance, unpaid principal balance	55	58
Impaired loan, total, unpaid principal balance	55	86
Impaired loan, total, related allowance	53	55
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	14	44
Impaired loan, with related allowance, average recorded investment	57	354
Impaired loan, total, average recorded investment	71	398
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	0	14
Impaired loan, with related allowance, interest income recognized	1	40
Impaired loan, total, interest income recognized	1	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	362	376
Impaired loan, with related allowance, recorded investment	0	0
Impaired loan, total, recorded investment	362	376
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	360	373
Impaired loan, with related allowance, unpaid principal balance	0	0
Impaired loan, total, unpaid principal balance	360	373
Impaired loan, total, related allowance	0	0
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	369	542
Impaired loan, with related allowance, average recorded investment	0	18
Impaired loan, total, average recorded investment	369	560
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	7	36
Impaired loan, with related allowance, interest income recognized	0	0
Impaired loan, total, interest income recognized	7	36
Residential | Real estate
Recorded Investment
Impaired loan, with no related allowance, recorded investment	634	646
Impaired loan, with related allowance, recorded investment	171	173
Impaired loan, total, recorded investment	805	819
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	634	646
Impaired loan, with related allowance, unpaid principal balance	171	173
Impaired loan, total, unpaid principal balance	805	819
Impaired loan, total, related allowance	9	9
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	640	875
Impaired loan, with related allowance, average recorded investment	176	342
Impaired loan, total, average recorded investment	816	1,217
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	7	29
Impaired loan, with related allowance, interest income recognized	2	9
Impaired loan, total, interest income recognized	9	38
Residential | Home equity
Recorded Investment
Impaired loan, with no related allowance, recorded investment	47	49
Impaired loan, with related allowance, recorded investment	0	0
Impaired loan, total, recorded investment	47	49
Unpaid Principal Balance
Impaired loan, with no related allowance, unpaid principal balance	47	49
Impaired loan, with related allowance, unpaid principal balance	0	0
Impaired loan, total, unpaid principal balance	47	49
Impaired loan, total, related allowance	0	0
Average Recorded Investment
Impaired loan, with no related allowance, average recorded investment	48	108
Impaired loan, with related allowance, average recorded investment	0	128
Impaired loan, total, average recorded investment	48	236
Interest Income Recognized
Impaired loan, with no related allowance, interest income recognized	2	10
Impaired loan, with related allowance, interest income recognized	0	1
Impaired loan, total, interest income recognized	2	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