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		6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($) troubled_debt_restructuring	Dec. 31, 2016 USD ($)
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | troubled_debt_restructuring				18
Loans modified in TDRs	$ 102,225		$ 102,225		$ 96,059
Modifications, Unfunded Commitments Available For Funding	1,400		1,400
Loans classified as TDRs, charge-offs	12,500	$ 500	15,100	$ 4,300
Financing receivable modifications recorded investment modified during period	20,913	5,188	27,020	6,817
Software/internet | Commercial Portfolio Segment
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	67,518		67,518		52,646
Financing receivable modifications recorded investment modified during period	16,135	4,402	22,242	5,525
Hardware | Commercial Portfolio Segment
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	5,582		5,582		14,870
Life science/healthcare | Commercial Portfolio Segment
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	25,385		25,385		24,176
Financing receivable modifications recorded investment modified during period	4,588	0	4,588	0
Premium wine | Commercial Portfolio Segment
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	3,304		3,304		3,194
Financing receivable modifications recorded investment modified during period	190	0	190	506
Other | Commercial Portfolio Segment
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	0		0		387
Other | Consumer Portfolio Segment
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	436		436		786
Financing receivable modifications recorded investment modified during period	0	786	0	786
Commercial loans
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period	20,913	$ 4,402	27,020	6,031
Commercial loans | Commercial Portfolio Segment
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	101,789		101,789		$ 95,273
Payment deferrals granted
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period	$ 20,900		$ 27,000	5,700
Principal Forgiveness [Member]
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period				$ 1,100