Loans and Allowance for Loan Losses Aging of Gross Loans, Broken out by Portfolio Segment and Class of Financing Receivable (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	$ 38,137	$ 51,649
Impaired Financing Receivable, Unpaid Principal Balance	42,899	73,271
30 - 59 Days Past Due	68,292	19,367
60 - 89 Days Past Due	4,176	12,572
Greater Than 90 Days Past Due	23,622	4,438
Total Past Due	96,090	36,377
Current	14,392,676	10,958,891
Loans Past Due 90 Days or More Still Accruing Interest	1,302	99
Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	33,287	27,618
Impaired Financing Receivable, Unpaid Principal Balance	34,218	28,316
30 - 59 Days Past Due	10,989	9,804
60 - 89 Days Past Due	1,627	1,291
Greater Than 90 Days Past Due	52	99
Total Past Due	12,668	11,194
Current	4,950,291	4,102,546
Loans Past Due 90 Days or More Still Accruing Interest	52	99
Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	2,521	19,667
Impaired Financing Receivable, Unpaid Principal Balance	2,535	35,317
30 - 59 Days Past Due	13,424	2,679
60 - 89 Days Past Due	126	3,965
Greater Than 90 Days Past Due	0	0
Total Past Due	13,550	6,644
Current	1,124,423	1,198,169
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Venture capital/private equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	0	40
Impaired Financing Receivable, Unpaid Principal Balance	0	40
30 - 59 Days Past Due	40,773	4
60 - 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	40,773	4
Current	4,580,526	2,408,382
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Life science
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	475	1,278
Impaired Financing Receivable, Unpaid Principal Balance	2,453	4,727
30 - 59 Days Past Due	738	395
60 - 89 Days Past Due	786	131
Greater Than 90 Days Past Due	0	0
Total Past Due	1,524	526
Current	1,298,728	1,179,462
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	1,304	1,442
Impaired Financing Receivable, Unpaid Principal Balance	1,743	1,778
30 - 59 Days Past Due	0	0
60 - 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	0	0
Current	795,345	665,755
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial, Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	233	690
Impaired Financing Receivable, Unpaid Principal Balance	233	718
30 - 59 Days Past Due	178	1,580
60 - 89 Days Past Due	3	142
Greater Than 90 Days Past Due	0	0
Total Past Due	181	1,722
Current	354,939	397,416
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	37,820	50,735
Impaired Financing Receivable, Unpaid Principal Balance	41,182	70,896
30 - 59 Days Past Due	66,102	14,462
60 - 89 Days Past Due	2,542	5,529
Greater Than 90 Days Past Due	52	99
Total Past Due	68,696	20,090
Current	13,104,252	9,951,730
Loans Past Due 90 Days or More Still Accruing Interest	52	99
Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	192	244
Impaired Financing Receivable, Unpaid Principal Balance	1,412	1,434
30 - 59 Days Past Due	1,592	240
60 - 89 Days Past Due	341	0
Greater Than 90 Days Past Due	1,250	0
Total Past Due	3,183	240
Current	1,114,286	872,586
Loans Past Due 90 Days or More Still Accruing Interest	1,250	0
Consumer, Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	125	670
Impaired Financing Receivable, Unpaid Principal Balance	305	941
30 - 59 Days Past Due	0	8
60 - 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	0	8
Current	160,212	98,965
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	317	914
Impaired Financing Receivable, Unpaid Principal Balance	1,717	2,375
30 - 59 Days Past Due	1,592	248
60 - 89 Days Past Due	341	0
Greater Than 90 Days Past Due	1,250	0
Total Past Due	3,183	248
Current	1,274,498	971,551
Loans Past Due 90 Days or More Still Accruing Interest	1,250	0
Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	67,694	14,710
60 - 89 Days Past Due	2,883	5,529
Greater Than 90 Days Past Due	1,302	99
Total Past Due	71,879	20,338
Current	14,378,750	10,923,281
Loans Past Due 90 Days or More Still Accruing Interest	1,302	99
Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	598	4,657
60 - 89 Days Past Due	1,293	7,043
Greater Than 90 Days Past Due	22,320	4,339
Total Past Due	24,211	16,039
Current	13,926	35,610
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Impaired Financing Receivables With Related Allowance [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	35,523	48,037
Impaired Financing Receivables With Related Allowance [Member] | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	33,287	27,308
Impaired Financing Receivables With Related Allowance [Member] | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	1,403	19,329
Impaired Financing Receivables With Related Allowance [Member] | Venture capital/private equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	0	40
Impaired Financing Receivables With Related Allowance [Member] | Life science
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	475	0
Impaired Financing Receivables With Related Allowance [Member] | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	0	0
Impaired Financing Receivables With Related Allowance [Member] | Commercial, Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	233	690
Impaired Financing Receivables With Related Allowance [Member] | Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	35,398	47,367
Impaired Financing Receivables With Related Allowance [Member] | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	0	0
Impaired Financing Receivables With Related Allowance [Member] | Consumer, Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	125	670
Impaired Financing Receivables With Related Allowance [Member] | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	125	670
Impaired Financing Receivables With No Related Allowance [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	2,614	3,612
Impaired Financing Receivables With No Related Allowance [Member] | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	0	310
Impaired Financing Receivables With No Related Allowance [Member] | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	1,118	338
Impaired Financing Receivables With No Related Allowance [Member] | Venture capital/private equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	0	0
Impaired Financing Receivables With No Related Allowance [Member] | Life science
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	0	1,278
Impaired Financing Receivables With No Related Allowance [Member] | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	1,304	1,442
Impaired Financing Receivables With No Related Allowance [Member] | Commercial, Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	0	0
Impaired Financing Receivables With No Related Allowance [Member] | Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	2,422	3,368
Impaired Financing Receivables With No Related Allowance [Member] | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	192	244
Impaired Financing Receivables With No Related Allowance [Member] | Consumer, Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	0	0
Impaired Financing Receivables With No Related Allowance [Member] | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Recorded Investment	$ 192	$ 244