Loans and Lease Finance Receivables and Allowance for Loan Losses - Summary of Activity Related to Troubled Debt Restructurings (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Financing Receivable, Modifications [Line Items]
Total TDRs	$ 7,273	$ 10,045	$ 7,273	$ 10,045
Performing TDRs [Member]
Financing Receivable, Modifications [Line Items]
Beginning balance	4,530	16,574	4,809	19,233
New modifications	0	0	311	3,143
Payoffs/payments, net and other	(777)	(10,839)	(1,367)	(13,826)
TDRs returned to accrual status	0	0	0	329
TDRs placed on nonaccrual status	0	0	0	(3,144)
Ending balance	3,753	5,735	3,753	5,735
Nonperforming TDRs [Member]
Financing Receivable, Modifications [Line Items]
Beginning balance	3,892	4,391	4,200	1,626
New modifications	278	0	316	2,066
Charge-offs	0	0	0	0
Payoffs/payments, net and other	(650)	(81)	(996)	(2,197)
TDRs returned to accrual status	0	0	0	(329)
TDRs placed on nonaccrual status	0	0	0	3,144
Ending balance	$ 3,520	$ 4,310	$ 3,520	$ 4,310