Loans and Allowance for Loan Losses - Recorded Investment in Loans Modified in TDRs (Detail) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	$ 496,000	[1]			$ 8,462,000	[1]
Loans classified as TDRs, charge-offs	0		1,200,000		0		2,400,000
Software
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	496,000		1,007,000		7,848,000		1,007,000
Hardware
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	0		6,330,000		0		7,783,000
Venture capital/private equity
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	0		0		0		88,000
Premium wine
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	0		0		614,000		0
Other
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	0		0		0		734,000
Commercial loans
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	496,000		7,337,000		8,462,000		9,612,000
Consumer loans
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	0		0		0		41,000
Consumer loans
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	0		0		0		41,000
Payment Deferrals Granted
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period			7,337,000	[1]	7,100,000		9,653,000	[1]
Forgiveness Of Principal
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period					$ 1,300,000

[1] There were no partial charge-offs on loans classified as TDRs for the three and nine months ended September 30, 2014. There were partial charge-offs of $1.2 million and $2.4 million on loans classified as TDRs for the three and nine months ended September 30, 2013