Allowance for Loan Losses - Summary of Roll Forward of Accruing and Nonaccrual TDRs (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($)
Financing Receivable, Impaired [Line Items]
Beginning Balance	$ 7,902	[1]
Ending Balance	7,495
Accruing
Financing Receivable, Impaired [Line Items]
Beginning Balance	4,115
Charge-offs	0
Payments and other adjustments	(584)
New TDR designation	52
Release TDR designation	0
Transfer	(69)
Ending Balance	3,514
Nonaccrual
Financing Receivable, Impaired [Line Items]
Beginning Balance	1,477
Charge-offs	0
Payments and other adjustments	(122)
Release TDR designation	0
Transfer	69
Ending Balance	1,424
Troubled Debt Restructuring
Financing Receivable, Impaired [Line Items]
Beginning Balance	5,592
Charge-offs	0
Payments and other adjustments	(706)
New TDR designation	52
Release TDR designation	0
Transfer	0
Ending Balance	$ 4,938

[1] Derived from audited December 31, 2018 Consolidated Financial Statements.