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	Sep. 30, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	$ 6,686	$ 19,367
60 - 89 Days Past Due	10,796	12,572
Greater Than 90 Days Past Due	1,187	4,438
Total Past Due	18,669	36,377
Current	12,093,805	10,958,891
Loans Past Due 90 Days or More Still Accruing Interest	125	99
Software
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	4,565	9,804
60 - 89 Days Past Due	4,334	1,291
Greater Than 90 Days Past Due	125	99
Total Past Due	9,024	11,194
Current	4,527,570	4,102,546
Loans Past Due 90 Days or More Still Accruing Interest	125	99
Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	247	2,679
60 - 89 Days Past Due	3,609	3,965
Greater Than 90 Days Past Due	0	0
Total Past Due	3,856	6,644
Current	1,078,234	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]
30 - 59 Days Past Due	5	4
60 - 89 Days Past Due	3	0
Greater Than 90 Days Past Due	0	0
Total Past Due	8	4
Current	2,948,327	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]
30 - 59 Days Past Due	265	395
60 - 89 Days Past Due	2,573	131
Greater Than 90 Days Past Due	0	0
Total Past Due	2,838	526
Current	1,253,292	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]
30 - 59 Days Past Due	5	0
60 - 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	5	0
Current	750,726	665,755
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	66	1,580
60 - 89 Days Past Due	65	142
Greater Than 90 Days Past Due	0	0
Total Past Due	131	1,722
Current	354,456	397,416
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	5,153	14,462
60 - 89 Days Past Due	10,584	5,529
Greater Than 90 Days Past Due	125	99
Total Past Due	15,862	20,090
Current	10,912,605	9,951,730
Loans Past Due 90 Days or More Still Accruing Interest	125	99
Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	1,250	240
60 - 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	1,250	240
Current	1,046,029	872,586
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	32	8
60 - 89 Days Past Due	1	0
Greater Than 90 Days Past Due	0	0
Total Past Due	33	8
Current	125,008	98,965
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	1,282	248
60 - 89 Days Past Due	1	0
Greater Than 90 Days Past Due	0	0
Total Past Due	1,283	248
Current	1,171,037	971,551
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	6,435	14,710
60 - 89 Days Past Due	10,585	5,529
Greater Than 90 Days Past Due	125	99
Total Past Due	17,145	20,338
Current	12,083,642	10,923,281
Loans Past Due 90 Days or More Still Accruing Interest	125	99
Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	251	4,657
60 - 89 Days Past Due	211	7,043
Greater Than 90 Days Past Due	1,062	4,339
Total Past Due	1,524	16,039
Current	10,163	35,610
Loans Past Due 90 Days or More Still Accruing Interest	$ 0	$ 0