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	Mar. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	$ 18,077	$ 10,563
60 - 89 Days Past Due	3,473	10,063
Greater Than 90 Days Past Due	13,965	2,288
Total Past Due	35,515	22,914
Current	8,887,314	9,001,334
Loans Past Due 90 Days or More Still Accruing Interest	36	19
Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	14,628	6,551
60 - 89 Days Past Due	1,733	387
Greater Than 90 Days Past Due	36	19
Total Past Due	16,397	6,957
Current	8,043,514	8,151,780
Loans Past Due 90 Days or More Still Accruing Interest	36	19
Commercial loans | Software
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	2,739	5,890
60 - 89 Days Past Due	1,493	238
Greater Than 90 Days Past Due	5	19
Total Past Due	4,237	6,147
Current	3,480,632	3,284,489
Loans Past Due 90 Days or More Still Accruing Interest	5	19
Commercial loans | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	4,034	167
60 - 89 Days Past Due	19	32
Greater Than 90 Days Past Due	31	0
Total Past Due	4,084	199
Current	1,206,431	1,107,422
Loans Past Due 90 Days or More Still Accruing Interest	31	0
Commercial loans | Venture capital/private equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	84	7
60 - 89 Days Past Due	1	0
Greater Than 90 Days Past Due	0	0
Total Past Due	85	7
Current	1,335,476	1,749,896
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	5,886	207
60 - 89 Days Past Due	220	117
Greater Than 90 Days Past Due	0	0
Total Past Due	6,106	324
Current	1,021,715	1,076,468
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	1,700	0
60 - 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	1,700	0
Current	600,383	554,886
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	185	280
60 - 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	185	280
Current	398,877	378,619
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	990	111
60 - 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	990	111
Current	817,582	827,121
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	605	0
60 - 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	605	0
Current	719,801	683,254
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Consumer loans | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	385	111
60 - 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	385	111
Current	97,781	143,867
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	15,618	6,662
60 - 89 Days Past Due	1,733	387
Greater Than 90 Days Past Due	36	19
Total Past Due	17,387	7,068
Current	8,861,096	8,978,901
Loans Past Due 90 Days or More Still Accruing Interest	36	19
Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	2,459	3,901
60 - 89 Days Past Due	1,740	9,676
Greater Than 90 Days Past Due	13,929	2,269
Total Past Due	18,128	15,846
Current	26,218	22,433
Loans Past Due 90 Days or More Still Accruing Interest	$ 0	$ 0