Loans and Allowance for Loan Losses - Average Impaired Loans, Broken out by Portfolio Segment and Class of Financing Receivable (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 41,419	$ 37,837
Commercial loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	37,614	21,971
Commercial loans | Software
Financing Receivable, Impaired [Line Items]
Average impaired loans	4,114	1,536
Commercial loans | Hardware
Financing Receivable, Impaired [Line Items]
Average impaired loans	23,632	12,262
Commercial loans | Life science
Financing Receivable, Impaired [Line Items]
Average impaired loans	314	146
Commercial loans | Premium wine
Financing Receivable, Impaired [Line Items]
Average impaired loans	4,336	3,383
Commercial loans | Other
Financing Receivable, Impaired [Line Items]
Average impaired loans	5,218	4,644
Consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	3,805	15,866
Consumer loans | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	2,676	12,847
Consumer loans | Consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 1,129	$ 3,019