Loans and Allowance for Loan Losses - Impaired Loans and Allowance for Loan Losses, Broken out by Portfolio Segment and Class of Financing Receivable (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	$ 24,989	$ 51,649
Total unpaid principal of impaired loans	32,724	73,271
Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	24,303	50,735
Total unpaid principal of impaired loans	30,562	70,896
Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	686	914
Total unpaid principal of impaired loans	2,162	2,375
Software
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	11,761	27,618
Total unpaid principal of impaired loans	12,002	28,316
Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	7,886	19,667
Total unpaid principal of impaired loans	9,505	35,317
Venture capital/private equity
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	40
Total unpaid principal of impaired loans	0	40
Life science
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	909	1,278
Total unpaid principal of impaired loans	4,892	4,727
Premium wine
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,408	1,442
Total unpaid principal of impaired loans	1,769	1,778
Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	2,339	690
Total unpaid principal of impaired loans	2,394	718
Real estate secured loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	236	244
Total unpaid principal of impaired loans	1,432	1,434
Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	450	670
Total unpaid principal of impaired loans	730	941
Impaired loans for which there is a related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	22,453	48,037
Impaired loans for which there is a related allowance for loan losses | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	22,003	47,367
Impaired loans for which there is a related allowance for loan losses | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	450	670
Impaired loans for which there is a related allowance for loan losses | Software
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	11,214	27,308
Impaired loans for which there is a related allowance for loan losses | Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	7,541	19,329
Impaired loans for which there is a related allowance for loan losses | Venture capital/private equity
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	40
Impaired loans for which there is a related allowance for loan losses | Life science
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	909	0
Impaired loans for which there is a related allowance for loan losses | Premium wine
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	0
Impaired loans for which there is a related allowance for loan losses | Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	2,339	690
Impaired loans for which there is a related allowance for loan losses | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	0
Impaired loans for which there is a related allowance for loan losses | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	450	670
Impaired loans for which there is no related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	2,536	3,612
Impaired loans for which there is no related allowance for loan losses | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	2,300	3,368
Impaired loans for which there is no related allowance for loan losses | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	236	244
Impaired loans for which there is no related allowance for loan losses | Software
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	547	310
Impaired loans for which there is no related allowance for loan losses | Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	345	338
Impaired loans for which there is no related allowance for loan losses | Venture capital/private equity
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	0
Impaired loans for which there is no related allowance for loan losses | Life science
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	1,278
Impaired loans for which there is no related allowance for loan losses | Premium wine
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,408	1,442
Impaired loans for which there is no related allowance for loan losses | Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	0
Impaired loans for which there is no related allowance for loan losses | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	236	244
Impaired loans for which there is no related allowance for loan losses | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	$ 0	$ 0