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		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 41,459	$ 35,300	$ 41,441	$ 36,569
Commercial loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	36,319	30,485	36,968	26,228
Commercial loans | Software
Financing Receivable, Impaired [Line Items]
Average impaired loans	5,473	1,896	4,794	1,716
Commercial loans | Hardware
Financing Receivable, Impaired [Line Items]
Average impaired loans	24,519	21,468	24,076	16,865
Commercial loans | Venture capital/private equity
Financing Receivable, Impaired [Line Items]
Average impaired loans	30	0	15	0
Commercial loans | Life science
Financing Receivable, Impaired [Line Items]
Average impaired loans	596	88	455	117
Commercial loans | Premium wine
Financing Receivable, Impaired [Line Items]
Average impaired loans	1,536	3,527	2,936	3,455
Commercial loans | Other
Financing Receivable, Impaired [Line Items]
Average impaired loans	4,165	3,506	4,692	4,075
Consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	5,140	4,815	4,473	10,341
Consumer loans | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	4,071	2,645	3,374	7,746
Consumer loans | Consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 1,069	$ 2,170	$ 1,099	$ 2,595