Allowance for Loan Losses - Summary of Roll Forward of Accruing and Nonaccrual TDRs (Detail) $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($)
Financing Receivable, Impaired [Line Items]
Beginning Balance	$ 7,770
Ending Balance	7,902
Accruing
Financing Receivable, Impaired [Line Items]
Beginning Balance	1,452
Charge-offs	0
Payments and other adjustments	(407)
New TDR designation	1,235
Release TDR designation	0
Transfer	1,835
Ending Balance	4,115
Nonaccrual
Financing Receivable, Impaired [Line Items]
Beginning Balance	2,612
Charge-offs	(92)
Payments and other adjustments	60
New TDR designation	732
Release TDR designation	0
Transfer	(1,835)
Ending Balance	1,477
Troubled Debt Restructuring
Financing Receivable, Impaired [Line Items]
Beginning Balance	4,064
Charge-offs	(92)
Payments and other adjustments	(347)
New TDR designation	1,967
Release TDR designation	0
Transfer	0
Ending Balance	$ 5,592

Amount of other addition (reduction) in allowance reserve for credit loss.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
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Amount of gain (loss) from converting allowance reserve for credit loss to currency of reporting entity from amount denominated or measured in a different currency, which decreases (increases) the allowance for loan and lease losses.

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Amount of addition to allowance reserve for credit loss arising from purchase of loan and lease portfolios.

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Amount of reduction of allowance reserve for credit loss arising from sale of loan and lease portfolios.

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Amount, after recoveries, of loans and leases that have been written-off.

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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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