Loans and Allowance for Loan Losses - Summary of Loans Modified in Troubled Debt Restructurings ("TDRs") by Portfolio Segment and Class of Financing Receivables (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	$ 33,900	$ 34,328
Commercial loans
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	31,085	31,028
Commercial loans | Software
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	1,751	2,021
Commercial loans | Hardware
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	19,749	20,514
Commercial loans | Venture capital/private equity
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	821	0
Commercial loans | Life science
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	454	0
Commercial loans | Premium wine
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	2,561	2,593
Commercial loans | Other
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	5,749	5,900
Consumer loans
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	2,845	3,300
Consumer loans | Real estate secured loans
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	1,753	2,199
Consumer loans | Consumer loans
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs	$ 1,092	$ 1,101