Loans, Allowance for Loan Losses and Allowance for Unfunded Credit Commitments - Summary of Recorded Investment in Loans Modified in TDRs (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]
Financing receivable modifications recorded investment modified during period	$ 10,398	$ 11,272	$ 32,647	$ 26,615
Loans classified as TDRs, charge-offs	13,000	0	21,500	2,600
Commercial loans
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period	10,398	11,272	32,325	26,615
Commercial loans | Software/internet
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period	0	10,876	14,069	26,034
Commercial loans | Hardware
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period	10,398	396	12,347	396
Commercial loans | Life science/healthcare
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period	0	0	5,909	0
Commercial loans | Premium wine
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period	0	0	0	185
Consumer loans | Other
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period	0	0	322	0
Payment deferrals granted
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period	$ 10,400	$ 11,300	$ 32,600	$ 26,600