Aging of Gross Loans, Broken out by Portfolio Segment and Class of Financing Receivable (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	$ 24,975	$ 4,765
60 - 89 Days Past Due	2,830	3,097
Greater Than 90 Days Past Due	7,953	6,613
Total Past Due	35,758	14,475
Current	8,230,410	7,015,846
Loans Past Due 90 Days or More Still Accruing Interest	5,000	0
Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	24,644	2,825
60 - 89 Days Past Due	2,329	1,303
Greater Than 90 Days Past Due	5,000	0
Total Past Due	31,973	4,128
Current	7,444,840	6,316,063
Loans Past Due 90 Days or More Still Accruing Interest	5,000	0
Commercial loans | Software
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	5,323	415
60 - 89 Days Past Due	273	1,006
Greater Than 90 Days Past Due	0	0
Total Past Due	5,596	1,421
Current	2,975,008	2,515,327
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial loans | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	8,901	1,951
60 - 89 Days Past Due	181	45
Greater Than 90 Days Past Due	5,000	0
Total Past Due	14,082	1,996
Current	1,163,848	954,690
Loans Past Due 90 Days or More Still Accruing Interest	5,000	0
Commercial loans | Venture capital/private equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	1,651	45
60 - 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	1,651	45
Current	1,406,695	1,128,475
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial loans | Life science
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	8,646	398
60 - 89 Days Past Due	1,875	78
Greater Than 90 Days Past Due	0	0
Total Past Due	10,521	476
Current	1,027,806	871,626
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial loans | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	49	1
60 - 89 Days Past Due	0	174
Greater Than 90 Days Past Due	0	0
Total Past Due	49	175
Current	512,621	475,406
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial loans | Commercial Other Financing Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	74	15
60 - 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	74	15
Current	358,862	370,539
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	0	590
60 - 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	0	590
Current	749,958	672,923
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Consumer loans | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
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	607,117	515,534
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Consumer loans | Consumer Other Financing Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	0	590
60 - 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	0	590
Current	142,841	157,389
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	24,644	3,415
60 - 89 Days Past Due	2,329	1,303
Greater Than 90 Days Past Due	5,000	0
Total Past Due	31,973	4,718
Current	8,194,798	6,988,986
Loans Past Due 90 Days or More Still Accruing Interest	5,000	0
Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	331	1,350
60 - 89 Days Past Due	501	1,794
Greater Than 90 Days Past Due	2,953	6,613
Total Past Due	3,785	9,757
Current	35,612	26,860
Loans Past Due 90 Days or More Still Accruing Interest	$ 0	$ 0