Loans and Allowance for Credit Losses - Schedule of Allowance for Credit Losses on Unfunded Loan Commitments (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($)
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Balance at beginning of period	$ 2,656
Expense (reversal of expense) for credit losses	1,745
Balance at end of period	8,950
Impact of ASC 326 Adoption
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Balance at beginning of period	4,549
Adjusted Balance
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Balance at end of period	$ 7,205