Related party transactions - Additional Information (Details) - USD ($)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Deposits from related parties	$ 238,781,000	$ 287,156,000
Aviation Time Sharing Agreement
Related Party Transaction [Line Items]
Payments to related party	266,000	208,000	$ 176,000
Registration Rights Agreement, 2016
Related Party Transaction [Line Items]
Payments to related party	0	671	0
Certain Executive Officers, Certain Management and Directors and Their Associates
Related Party Transaction [Line Items]
Unfunded commitments	19,404,000	15,000,000
Director
Related Party Transaction [Line Items]
Unamortized leasehold improvements	86,000	116,000
Lease expense	$ 509,000	$ 516,000	$ 504,000

Amount before accumulated depreciation of additions or improvements to assets held under a lease arrangement.

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Amount of unfunded portion of contractual agreement to lend funds to borrower for financing receivable modified as troubled debt restructuring.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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Amount of operating lease expense. Excludes sublease income.

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