Credit Quality Indicators, Broken out by Portfolio Segment and Class of Financing Receivables (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 8,266,168	$ 7,030,321
Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	7,512,582	6,335,392
Commercial loans | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,983,420	2,517,890
Commercial loans | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,205,059	961,869
Commercial loans | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,408,346	1,128,520
Commercial loans | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,038,327	872,413
Commercial loans | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	515,749	478,793
Commercial loans | Commercial Other Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	361,681	375,907
Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	753,586	694,929
Consumer loans | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	609,525	533,817
Consumer loans | Consumer Other Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	144,061	161,112
Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	7,723,983	6,434,133
Pass | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	7,003,757	5,785,972
Pass | Commercial loans | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,751,238	2,290,497
Pass | Commercial loans | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,069,973	839,230
Pass | Commercial loans | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,406,746	1,120,373
Pass | Commercial loans | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	939,092	748,129
Pass | Commercial loans | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	501,507	434,309
Pass | Commercial loans | Commercial Other Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	335,201	353,434
Pass | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	720,226	648,161
Pass | Consumer loans | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	588,678	497,060
Pass | Consumer loans | Consumer Other Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	131,548	151,101
Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	502,788	559,571
Performing (Criticized) | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	473,056	534,219
Performing (Criticized) | Commercial loans | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	229,366	226,251
Performing (Criticized) | Commercial loans | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	107,957	117,456
Performing (Criticized) | Commercial loans | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,600	8,147
Performing (Criticized) | Commercial loans | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	99,235	123,973
Performing (Criticized) | Commercial loans | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	11,163	41,272
Performing (Criticized) | Commercial loans | Commercial Other Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	23,735	17,120
Performing (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	29,732	25,352
Performing (Criticized) | Consumer loans | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	18,439	18,474
Performing (Criticized) | Consumer loans | Consumer Other Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	11,293	6,878
Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	39,397	36,617
Impaired | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	35,769	15,201
Impaired | Commercial loans | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,816	1,142
Impaired | Commercial loans | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	27,129	5,183
Impaired | Commercial loans | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	0
Impaired | Commercial loans | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	311
Impaired | Commercial loans | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,079	3,212
Impaired | Commercial loans | Commercial Other Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,745	5,353
Impaired | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,628	21,416
Impaired | Consumer loans | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,408	18,283
Impaired | Consumer loans | Consumer Other Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 1,220	$ 3,133