Credit Quality Indicators, Broken out by Portfolio Segment and Class of Financing Receivables (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 7,180,779	$ 7,030,321
Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	6,473,631	6,335,392
Commercial loans | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,536,362	2,517,890
Commercial loans | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,064,742	961,869
Commercial loans | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,134,631	1,128,520
Commercial loans | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	872,344	872,413
Commercial loans | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	482,808	478,793
Commercial loans | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	382,744	375,907
Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	707,148	694,929
Consumer loans | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	542,402	533,817
Consumer loans | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	164,746	161,112
Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	6,562,500	6,434,133
Pass | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	5,891,550	5,785,972
Pass | Commercial loans | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,304,838	2,290,497
Pass | Commercial loans | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	931,590	839,230
Pass | Commercial loans | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,128,482	1,120,373
Pass | Commercial loans | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	737,956	748,129
Pass | Commercial loans | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	460,232	434,309
Pass | Commercial loans | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	328,452	353,434
Pass | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	670,950	648,161
Pass | Consumer loans | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	515,071	497,060
Pass | Consumer loans | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	155,879	151,101
Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	576,582	559,571
Performing (Criticized) | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	546,369	534,219
Performing (Criticized) | Commercial loans | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	229,956	226,251
Performing (Criticized) | Commercial loans | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	106,921	117,456
Performing (Criticized) | Commercial loans | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	6,149	8,147
Performing (Criticized) | Commercial loans | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	134,250	123,973
Performing (Criticized) | Commercial loans | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	18,807	41,272
Performing (Criticized) | Commercial loans | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	50,286	17,120
Performing (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	30,213	25,352
Performing (Criticized) | Consumer loans | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	24,327	18,474
Performing (Criticized) | Consumer loans | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	5,886	6,878
Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	41,697	36,617
Impaired | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	35,712	15,201
Impaired | Commercial loans | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,568	1,142
Impaired | Commercial loans | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	26,231	5,183
Impaired | Commercial loans | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	138	311
Impaired | Commercial loans | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,769	3,212
Impaired | Commercial loans | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,006	5,353
Impaired | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	5,985	21,416
Impaired | Consumer loans | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,004	18,283
Impaired | Consumer loans | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 2,981	$ 3,133