Loans and Allowance for Loan Losses - Summary of Non Accrual Loan (Parenthetical) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest foregone life-to-date	$ 2,744	$ 1,952	$ 12,485	[1]
Amount of foregone interest applied to principal life-to-date	$ 471	$ 1,214	3,495	[1]
Non Accrual Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non accrual loans			32,668
Interest collected on nonaccrual loans recorded			795
Interest paid			917
Interest foregone life-to-date			1,487
Amount of foregone interest applied to principal life-to-date			$ 1,221

[1] Does not include the Bank’s nonaccrual loans of $32,668, interest income foregone for the year of $795 and foregone interest paid and applied to principal for the year of $917, interest income foregone life-to-date of $1,487 and foregone interest paid and applied to principal life-to-date of $1,221.