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		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period	$ 22,968	$ 20,913	$ 26,017	$ 27,020
Loans classified as TDRs, charge-offs	8,500	12,500	8,500	15,100
Private equity/venture capital
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period	0	0
Commercial loans
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period	22,968	20,913	25,692	27,020
Commercial loans | Software/internet
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period	14,783	16,135	14,783	22,242
Commercial loans | Hardware
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period	1,954	0	3,448	0
Commercial loans | Private equity/venture capital
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period			0	0
Commercial loans | Life science/healthcare
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period	6,231	4,588	7,461	4,588
Commercial loans | Premium wine
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period	0	190	0	190
Consumer loans
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period	0	0	325	0
Consumer loans | Other
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period	0	0	325	0
Payment deferrals granted
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period	$ 23,000	$ 20,900	$ 26,000	$ 27,000