Purchased Loans - Additional Information (Details)	12 Months Ended
Dec. 31, 2018 USD ($) loan	Dec. 31, 2017 USD ($) loan	Dec. 31, 2016 USD ($)
Financing Receivable, Allowance for Credit Losses [Line Items]
Restructured loans discontinued past due period	90 days
Allowance for loan losses attributable to restructured loans	$ 49,026,000	$ 46,211,000
Purchased
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonperforming loans charged off past due period	90 days
Number of restructured loans \| loan	8	3
Restructured loans discontinued past due period	90 days	90 days
Average recorded investment in impaired loans	$ 9,396,000	$ 7,687,000	$ 6,594,000
Interest income recognized on impaired loans			168,000
Interest income recognized on credit-deteriorated loans	119,000	234,000
Modifications, recorded investment	7,495,000	8,965,000	$ 4,028,000
Modifications, subsequent default, recorded investment	212,000	54,000
Remaining availability under commitments to lend additional funds on restructured loans	3,000	9,000
Purchased \| Nonaccruing Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Outstanding balance of restructured loans	413,000	128,000
Purchased \| Restructured Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Outstanding balance of restructured loans	1,868,000	523,000
Allowance for loan losses attributable to restructured loans	$ 58,000	$ 103,000

Nonperforming loans charged off past due period.

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Number of Restructured Loans

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Maximum duration past due for restructured loans to be considered performing.

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The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

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Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

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Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

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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 allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Reflects the unfunded portion of contractual agreements to lend funds to borrowers for loans whose terms have been modified by troubled debt restructuring.

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The amount of interest income on impaired and nonperforming loans that is due to the change in present value attributable to the passage of time.

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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes loans held for sale. Excludes loans and leases covered under loss sharing agreements.

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