Loans and Lease Finance Receivables and Allowance for Loan Losses - Schedule of Recorded Investment in, and Aging of, Past Due and Nonaccrual Loans, Excluding PCI Loans by Class of Loans (Parenthetical) (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccruing loans, current	$ 2,600	$ 3,600
Nonaccrual loans	8,600
30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual	562
60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual	1,300	376
90+ Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual	$ 12,000	$ 6,800