Loans, Allowance for Loan Losses and Allowance for Unfunded Credit Commitments - Summary of Loans Modified in Troubled Debt Restructurings ("TDRs") by Portfolio Segment and Class of Financing Receivables (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($) troubled_debt_restructuring	Dec. 31, 2016 USD ($)
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | troubled_debt_restructuring		21
Loans modified in TDRs	$ 95,413		$ 96,059
Modifications, Unfunded Commitments Available For Funding	2,900
Loans classified as TDRs, charge-offs	6,200	$ 3,800
Financing receivable modifications recorded investment modified during period	6,309	11,359
Software/internet | Commercial Portfolio Segment
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	59,419		52,646
Financing receivable modifications recorded investment modified during period	6,309	10,854
Hardware | Commercial Portfolio Segment
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	10,687		14,870
Life science/healthcare | Commercial Portfolio Segment
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	21,561		24,176
Premium wine | Commercial Portfolio Segment
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	3,177		3,194
Other | Commercial Portfolio Segment
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	33		387
Financing receivable modifications recorded investment modified during period	0	505
Other | Consumer Portfolio Segment
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	536		786
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	6,309	11,359
Commercial loans | Commercial Portfolio Segment
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	94,877		95,273
Consumer loans | Consumer Portfolio Segment
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	536		$ 786
Payment deferrals granted
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period	6,300	$ 2,400
Principal Forgiveness [Member]
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period	$ 9,000