Loans, Allowance for Credit Losses - Loans, and Credit Quality - Summary of allowance for loan losses (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 13,972	$ 13,153	$ 13,153
Provision for credit losses	3,000	200	1,200
Charge-offs	(93)	(10)	(927)
Recoveries	38	27	546
Net (charge-offs) recoveries	(55)	17	(381)
Ending balance	26,202	$ 13,370	13,972
Adoption of CECL
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	8,488
Ending balance			8,488
Initial PCD ACL
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	797
Ending balance			797
Total impact for adoption of CECL
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 9,285
Ending balance			$ 9,285

Amount, after recovery, of writeoff of financing receivable, charged against allowance for credit loss.

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Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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Amount of recovery of financing receivables doubtful of collection that were previously charged off.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of writeoff of financing receivable, charged against allowance for credit loss.

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Amount of credit loss expense (reversal of expense) for financing receivable.

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