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	Sep. 30, 2014	Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	$ 11,687	$ 51,649
Total unpaid principal of impaired loans	17,561	73,271
Software
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	8,730	27,618
Total unpaid principal of impaired loans	12,069	28,316
Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans		19,667
Total unpaid principal of impaired loans		35,317
Venture capital/private equity
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans		40
Total unpaid principal of impaired loans		40
Life science
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,000	1,278
Total unpaid principal of impaired loans	1,000	4,727
Premium wine
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,339	1,442
Total unpaid principal of impaired loans	1,752	1,778
Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	11,255	50,735
Total unpaid principal of impaired loans	15,619	70,896
Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	186	690
Total unpaid principal of impaired loans	798	718
Real estate secured loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	208	244
Total unpaid principal of impaired loans	1,416	1,434
Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	224	670
Total unpaid principal of impaired loans	526	941
Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	432	914
Total unpaid principal of impaired loans	1,942	2,375
Impaired loans for which there is a related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	10,140	48,037
Impaired loans for which there is a related allowance for loan losses | Software
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	8,730	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		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		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	1,000	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 | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	9,916	47,367
Impaired loans for which there is a related allowance for loan losses | Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	186	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	224	670
Impaired loans for which there is a related allowance for loan losses | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	224	670
Impaired loans for which there is no related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,547	3,612
Impaired loans for which there is no related allowance for loan losses | Software
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	310
Impaired loans for which there is no related allowance for loan losses | Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans		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
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	1,339	1,442
Impaired loans for which there is no related allowance for loan losses | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,339	3,368
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	208	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
Impaired loans for which there is no related allowance for loan losses | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	$ 208	$ 244