Loans and Allowance for Loan Losses - Recorded Investment in Loans Modified in TDRs (Detail) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	$ 6,496,000	[1]	$ 13,571,000	[1]	$ 7,153,000	[1]	$ 16,424,000	[1]
Loans classified as TDRs, charge-offs	1,200,000		10,000,000				10,900,000
Commercial loans
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	6,496,000		13,282,000		7,083,000		16,013,000
Commercial loans | Software
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	778,000		0		778,000		100,000
Commercial loans | Hardware
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	5,629,000		12,747,000		5,629,000		13,198,000
Commercial loans | Venture capital/private equity
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	89,000		0		676,000		0
Commercial loans | Premium wine
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	0		0		0		275,000
Commercial loans | Other
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	0		535,000		0		2,440,000
Consumer loans
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	0		289,000		70,000		411,000
Consumer loans | Real estate secured loans
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	0		289,000		0		411,000
Consumer loans | Consumer loans
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	0		0		70,000		0
Payment Deferrals Granted
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	6,500,000		3,600,000		7,200,000		6,300,000
Forgiveness Of Principal
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period			$ 10,000,000				$ 10,100,000

[1] the three and six months ended June 30, 2013. There were partial charge-offs of $10.0 million and $10.9 million, respectively, on loans classified as TDRs during the three and six months ended June 30, 2012.