Loans and Allowance for Loan Losses - Allowance for Loan Losses Individually and Collectively Evaluated for Impairment (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	$ 7,728	$ 6,261
Collectively Evaluated for Impairment	104,477	104,390
Commercial loans
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	7,304	6,013
Collectively Evaluated for Impairment	97,677	97,400
Commercial loans | Software
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	2,087	762
Collectively Evaluated for Impairment	42,923	41,886
Commercial loans | Hardware
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	5,016	5,251
Collectively Evaluated for Impairment	22,853	24,510
Commercial loans | Venture capital/private equity
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	0	0
Collectively Evaluated for Impairment	10,482	9,963
Commercial loans | Life science
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	201	0
Collectively Evaluated for Impairment	13,745	13,606
Commercial loans | Premium wine
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	0	0
Collectively Evaluated for Impairment	3,699	3,523
Commercial loans | Other
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	0	0
Collectively Evaluated for Impairment	3,975	3,912
Consumer loans
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	424	248
Collectively Evaluated for Impairment	$ 6,800	$ 6,990