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		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) troubled_debt_restructuring	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | troubled_debt_restructuring			18
Loans modified in TDRs	$ 87,438		$ 87,438		$ 96,059
Modifications, Unfunded Commitments Available For Funding	1,200		1,200
Loans classified as TDRs, charge-offs	0	$ 700	2,600	$ 3,500
Financing receivable modifications recorded investment modified during period	11,272	12,121	26,615	17,893
Software/internet | Commercial Portfolio Segment
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	63,326		63,326		52,646
Financing receivable modifications recorded investment modified during period	10,876	78	26,034	4,569
Hardware | Commercial Portfolio Segment
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	395		395		14,870
Financing receivable modifications recorded investment modified during period	396	10,329	396	10,329
Life science/healthcare | Commercial Portfolio Segment
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	20,015		20,015		24,176
Financing receivable modifications recorded investment modified during period	0	1,714	0	1,714
Premium wine | Commercial Portfolio Segment
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	3,265		3,265		3,194
Financing receivable modifications recorded investment modified during period	0	0	185	495
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	437		437		786
Financing receivable modifications recorded investment modified during period	0	0	0	786
Commercial loans
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period	11,272	12,121	26,615	17,107
Commercial loans | Commercial Portfolio Segment
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	87,001		87,001		$ 95,273
Payment deferrals granted
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period	$ 11,300	12,000	$ 26,600	17,600
Principal Forgiveness [Member]
Financing Receivable, Modifications [Line Items]
Financing receivable modifications recorded investment modified during period		$ 100		$ 300