Allowance for Loan Losses - Summary of Roll Forward of Accruing and Nonaccrual TDRs (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Financing Receivable, Impaired [Line Items]
Beginning Balance	$ 7,902	[1]
Ending Balance	7,858
Accruing
Financing Receivable, Impaired [Line Items]
Beginning Balance	4,115
Charge-offs	0
Payments and other adjustments	(21)
Release TDR designation	0
Transfer	(616)
Ending Balance	3,478
Nonaccrual
Financing Receivable, Impaired [Line Items]
Beginning Balance	1,477
Charge-offs	0
Payments and other adjustments	(6)
Release TDR designation	0
Transfer	616
Ending Balance	2,087
Troubled Debt Restructuring
Financing Receivable, Impaired [Line Items]
Beginning Balance	5,592
Charge-offs	0
Payments and other adjustments	(27)
Release TDR designation	0
Transfer	0
Ending Balance	$ 5,565

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