Impaired Loans and the Allowance for Loan Losses, Broken out by Portfolio Segment and Class of Financing Receivable (Detail) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	$ 40,506	$ 39,426
Total unpaid principal of impaired loans	52,024	46,950
Software | Commercial loans | Impaired loans for which there is a related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	2,322	2,958
Hardware | Commercial loans | Impaired loans for which there is a related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	5,398	3,517
Life science | Commercial loans | Impaired loans for which there is a related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	633	2,050
Premium wine | Commercial loans | Impaired loans for which there is a related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,993	2,995
Other | Commercial loans | Impaired loans for which there is a related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	5,435	1,158
Other | Consumer loans | Impaired loans for which there is a related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	3,322
Commercial loans | Impaired loans for which there is a related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	15,781	12,678
Consumer loans | Real estate secured loans | Impaired loans for which there is a related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	18,382	20,559
Consumer loans | Impaired loans for which there is a related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	21,704	20,559
Impaired loans for which there is a related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	37,485	33,237
Software | Commercial loans | Impaired loans for which there is no related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	237	334
Hardware | Commercial loans | Impaired loans for which there is no related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans		307
Life science | Commercial loans | Impaired loans for which there is no related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans		1,362
Premium wine | Commercial loans | Impaired loans for which there is no related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,264	3,167
Other | Commercial loans | Impaired loans for which there is no related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,158	1,019
Commercial loans | Impaired loans for which there is no related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	2,659	6,189
Consumer loans | Real estate secured loans | Impaired loans for which there is no related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	362
Consumer loans | Impaired loans for which there is no related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	362
Impaired loans for which there is no related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	3,021	6,189
Software | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	2,559	3,292
Total unpaid principal of impaired loans	3,585	5,237
Hardware | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	5,398	3,824
Total unpaid principal of impaired loans	8,579	3,931
Life science | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	633	3,412
Total unpaid principal of impaired loans	825	4,433
Premium wine | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	3,257	6,162
Total unpaid principal of impaired loans	3,350	7,129
Other | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	6,593	2,177
Total unpaid principal of impaired loans	9,828	2,790
Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	18,440	18,867
Total unpaid principal of impaired loans	26,167	23,520
Other | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	3,322
Total unpaid principal of impaired loans	3,322
Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	22,066	20,559
Total unpaid principal of impaired loans	25,857	23,430
Consumer loans | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	18,744	20,559
Total unpaid principal of impaired loans	$ 22,535	$ 23,430