Aging of Gross Loans, Broken out by Portfolio Segment and Class of Financing Receivable (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	$ 27,853	$ 4,765
60 - 89 Days Past Due	444	3,097
Greater Than 90 Days Past Due	6,637	6,613
Total Past Due	34,934	14,475
Current	7,145,845	7,015,846
Loans Past Due 90 Days or More Still Accruing Interest
Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	27,817	2,825
60 - 89 Days Past Due	306	1,303
Total Past Due	28,123	4,128
Current	6,409,796	6,316,063
Loans Past Due 90 Days or More Still Accruing Interest
Commercial loans | Software
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	750	415
60 - 89 Days Past Due	121	1,006
Total Past Due	871	1,421
Current	2,533,923	2,515,327
Loans Past Due 90 Days or More Still Accruing Interest
Commercial loans | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	4,549	1,951
60 - 89 Days Past Due	7	45
Total Past Due	4,556	1,996
Current	1,033,955	954,690
Loans Past Due 90 Days or More Still Accruing Interest
Commercial loans | Venture capital/private equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	2,843	45
Total Past Due	2,843	45
Current	1,131,788	1,128,475
Loans Past Due 90 Days or More Still Accruing Interest
Commercial loans | Life science
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	13,717	398
60 - 89 Days Past Due	171	78
Total Past Due	13,888	476
Current	858,318	871,626
Loans Past Due 90 Days or More Still Accruing Interest
Commercial loans | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due		1
60 - 89 Days Past Due		174
Total Past Due		175
Current	479,039	475,406
Loans Past Due 90 Days or More Still Accruing Interest
Commercial loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	5,958	15
60 - 89 Days Past Due	7
Total Past Due	5,965	15
Current	372,773	370,539
Loans Past Due 90 Days or More Still Accruing Interest
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due		590
Total Past Due		590
Current	701,163	672,923
Loans Past Due 90 Days or More Still Accruing Interest
Consumer loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due		590
Total Past Due		590
Current	161,765	157,389
Loans Past Due 90 Days or More Still Accruing Interest
Consumer loans | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	539,398	515,534
Loans Past Due 90 Days or More Still Accruing Interest
Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	27,817	3,415
60 - 89 Days Past Due	306	1,303
Total Past Due	28,123	4,718
Current	7,110,959	6,988,986
Loans Past Due 90 Days or More Still Accruing Interest
Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	36	1,350
60 - 89 Days Past Due	138	1,794
Greater Than 90 Days Past Due	6,637	6,613
Total Past Due	6,811	9,757
Current	34,886	26,860
Loans Past Due 90 Days or More Still Accruing Interest