Allowance for Loan Losses - Summary of Roll Forward of Accruing and Nonaccrual TDRs (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($)
Financing Receivable, Impaired [Line Items]
Beginning Balance	$ 7,902	[1]
Ending Balance	7,479
Accruing
Financing Receivable, Impaired [Line Items]
Beginning Balance	4,115
Charge-offs	0
Payments and other adjustments	(52)
New TDR designation	52
Release TDR designation	0
Transfer	(69)
Ending Balance	4,046
Nonaccrual
Financing Receivable, Impaired [Line Items]
Beginning Balance	1,477
Charge-offs	0
Payments and other adjustments	(106)
Release TDR designation	0
Transfer	69
Ending Balance	1,440
Troubled Debt Restructuring
Financing Receivable, Impaired [Line Items]
Beginning Balance	5,592
Charge-offs	0
Payments and other adjustments	(158)
New TDR designation	52
Release TDR designation	0
Transfer	0
Ending Balance	$ 5,486

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