Loans and Allowance - Impaired financing receivables (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Recorded Investment with specific reserves	$ 26	$ 89
Unpaid Principal Balance with specific reserves	41	293
Interest Income Recognized with specific reserves	2	15
Specific Reserve with specific reserves	15	226
Recorded Investment	50	347
Recorded Investment with no specific reserve	4,627	2,435
Unpaid Principal Balance with no specific reserve	5,396	3,204
Interest Income Recognized with no specific reserve	109	45
Specific Reserve	20	230
Average Recorded Investment with no specific reserve	5,895	3,179
Consumer
Financing Receivable, Impaired [Line Items]
Recorded Investment with specific reserves	26	89
Unpaid Principal Balance with specific reserves	41	89
Interest Income Recognized with specific reserves	2	3
Specific Reserve with specific reserves	15	22
Recorded Investment	50	136
Recorded Investment with no specific reserve	123	116
Unpaid Principal Balance with no specific reserve	123	116
Interest Income Recognized with no specific reserve	6
Residential real estate
Financing Receivable, Impaired [Line Items]
Recorded Investment with no specific reserve	96	96
Unpaid Principal Balance with no specific reserve	96	96
Interest Income Recognized with no specific reserve	8	2
Average Recorded Investment with no specific reserve	122	50
Commercial
Financing Receivable, Impaired [Line Items]
Specific Reserve with specific reserves		204
Recorded Investment with no specific reserve	3,680	1,267
Unpaid Principal Balance with no specific reserve	3,680	1,267
Interest Income Recognized with no specific reserve	81	39
Average Recorded Investment with no specific reserve	3,845	1,148
Commercial Mortgage Portfolio Segment
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance with specific reserves		204
Interest Income Recognized with specific reserves		12
Specific Reserve with specific reserves		204
Recorded Investment		211
Recorded Investment with no specific reserve	728	956
Unpaid Principal Balance with no specific reserve	1,497	1,725
Interest Income Recognized with no specific reserve	14	4
Average Recorded Investment with no specific reserve	$ 1,928	$ 1,981

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524

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Amount of allowance for credit losses related to recorded investment.

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Amount of average investment of impaired financing receivables for which there is no related allowance for credit losses.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Amount of interest income, recognized on cash basis, on financing receivables, for which there is no related allowance for credit losses and are recognized as impaired.

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Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Amount of average investment of impaired financing receivables for which there is a related allowance for credit losses.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5258-111524

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