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	Jun. 30, 2014	Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	$ 22,346	$ 51,649
Total unpaid principal of impaired loans	25,904	73,271
Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	21,790	50,735
Total unpaid principal of impaired loans	23,852	70,896
Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	556	914
Total unpaid principal of impaired loans	2,052	2,375
Software
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	14,416	27,618
Total unpaid principal of impaired loans	15,747	28,316
Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	5,502	19,667
Total unpaid principal of impaired loans	5,793	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	0	1,278
Total unpaid principal of impaired loans	0	4,727
Premium wine
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,373	1,442
Total unpaid principal of impaired loans	1,761	1,778
Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	499	690
Total unpaid principal of impaired loans	551	718
Real estate secured loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	220	244
Total unpaid principal of impaired loans	1,424	1,434
Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	336	670
Total unpaid principal of impaired loans	628	941
Impaired loans for which there is a related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	19,956	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	19,620	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	336	670
Impaired loans for which there is a related allowance for loan losses | Software
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	13,619	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	5,502	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	0	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	499	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	336	670
Impaired loans for which there is no related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	2,390	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	2,170	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	220	244
Impaired loans for which there is no related allowance for loan losses | Software
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	797	310
Impaired loans for which there is no related allowance for loan losses | Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	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	1,373	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	220	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