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	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	$ 38,137	$ 51,649
Impaired Financing Receivable, Unpaid Principal Balance	42,899	73,271
Software and internet
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	33,287	27,618
Impaired Financing Receivable, Unpaid Principal Balance	34,218	28,316
Hardware
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	2,521	19,667
Impaired Financing Receivable, Unpaid Principal Balance	2,535	35,317
Venture capital/private equity
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	0	40
Impaired Financing Receivable, Unpaid Principal Balance	0	40
Life science
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	475	1,278
Impaired Financing Receivable, Unpaid Principal Balance	2,453	4,727
Premium wine
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	1,304	1,442
Impaired Financing Receivable, Unpaid Principal Balance	1,743	1,778
Commercial, Other
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	233	690
Impaired Financing Receivable, Unpaid Principal Balance	233	718
Commercial loans
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	37,820	50,735
Impaired Financing Receivable, Unpaid Principal Balance	41,182	70,896
Real estate secured loans
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	192	244
Impaired Financing Receivable, Unpaid Principal Balance	1,412	1,434
Consumer, Other
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	125	670
Impaired Financing Receivable, Unpaid Principal Balance	305	941
Consumer loans
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	317	914
Impaired Financing Receivable, Unpaid Principal Balance	1,717	2,375
Impaired Financing Receivables With No Related Allowance [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	2,614	3,612
Impaired Financing Receivables With No Related Allowance [Member] | Software and internet
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	0	310
Impaired Financing Receivables With No Related Allowance [Member] | Hardware
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	1,118	338
Impaired Financing Receivables With No Related Allowance [Member] | Venture capital/private equity
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	0	0
Impaired Financing Receivables With No Related Allowance [Member] | Life science
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	0	1,278
Impaired Financing Receivables With No Related Allowance [Member] | Premium wine
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	1,304	1,442
Impaired Financing Receivables With No Related Allowance [Member] | Commercial, Other
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	0	0
Impaired Financing Receivables With No Related Allowance [Member] | Commercial loans
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	2,422	3,368
Impaired Financing Receivables With No Related Allowance [Member] | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	192	244
Impaired Financing Receivables With No Related Allowance [Member] | Consumer, Other
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	0	0
Impaired Financing Receivables With No Related Allowance [Member] | Consumer loans
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	192	244
Impaired Financing Receivables With Related Allowance [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	35,523	48,037
Impaired Financing Receivables With Related Allowance [Member] | Software and internet
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	33,287	27,308
Impaired Financing Receivables With Related Allowance [Member] | Hardware
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	1,403	19,329
Impaired Financing Receivables With Related Allowance [Member] | Venture capital/private equity
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	0	40
Impaired Financing Receivables With Related Allowance [Member] | Life science
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	475	0
Impaired Financing Receivables With Related Allowance [Member] | Premium wine
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	0	0
Impaired Financing Receivables With Related Allowance [Member] | Commercial, Other
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	233	690
Impaired Financing Receivables With Related Allowance [Member] | Commercial loans
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	35,398	47,367
Impaired Financing Receivables With Related Allowance [Member] | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	0	0
Impaired Financing Receivables With Related Allowance [Member] | Consumer, Other
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	125	670
Impaired Financing Receivables With Related Allowance [Member] | Consumer loans
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	$ 125	$ 670