Allowance for Loan Losses Individually and Collectively Evaluated for Impairment (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	$ 6,003	$ 3,707
Collectively Evaluated for Impairment	95,521	86,240
Commercial loans
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	5,714	2,967
Collectively Evaluated for Impairment	88,440	79,399
Commercial loans | Software
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	653	526
Collectively Evaluated for Impairment	36,592	37,737
Commercial loans | Hardware
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	5,061	1,261
Collectively Evaluated for Impairment	22,624	15,549
Commercial loans | Venture capital/private equity
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	0	0
Collectively Evaluated for Impairment	10,643	7,319
Commercial loans | Life science
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	0	0
Collectively Evaluated for Impairment	12,163	10,243
Commercial loans | Premium wine
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	0	0
Collectively Evaluated for Impairment	3,161	3,914
Commercial loans | Commercial Other Financing Receivable
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	0	1,180
Collectively Evaluated for Impairment	3,257	4,637
Consumer loans
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	289	740
Collectively Evaluated for Impairment	$ 7,081	$ 6,841