Loans and Allowance for Credit Losses - Schedule of Allowance for Credit Losses on Unfunded Loan Commitments (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Balance at beginning of period	$ 8,950	$ 2,656
Expense (reversal of expense) for credit losses	2,076	3,821
Balance at end of period	$ 11,026	11,026
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 beginning of period		$ 7,205