Loans and Allowance for Loan Losses - Credit Quality Indicators, Broken out by Portfolio Segment and Class of Financing Receivables (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 10,920,482	$ 10,995,268
Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	9,902,338	10,022,555
Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,018,144	972,713
Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,164,435	4,141,358
Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,204,350	1,224,480
Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,221,772	2,408,426
Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,182,219	1,181,266
Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	703,778	667,197
Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	425,784	399,828
Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	916,779	873,070
Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	101,365	99,643
Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	10,317,284	10,371,201
Pass | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	9,306,512	9,406,826
Pass | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,010,772	964,375
Pass | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,859,696	3,875,043
Pass | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,023,405	995,055
Pass | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,221,772	2,408,386
Pass | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,097,180	1,091,993
Pass | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	693,351	652,747
Pass | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	411,108	383,602
Pass | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	912,790	868,789
Pass | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	97,982	95,586
Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	578,209	572,418
Performing (Criticized) | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	571,523	564,994
Performing (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	6,686	7,424
Performing (Criticized) | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	292,978	238,697
Performing (Criticized) | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	173,059	209,758
Performing (Criticized) | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	0
Performing (Criticized) | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	84,130	87,995
Performing (Criticized) | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	9,019	13,008
Performing (Criticized) | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	12,337	15,536
Performing (Criticized) | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,753	4,037
Performing (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,933	3,387
Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	24,989	51,649
Impaired | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	24,303	50,735
Impaired | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	686	914
Impaired | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	11,761	27,618
Impaired | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	7,886	19,667
Impaired | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	40
Impaired | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	909	1,278
Impaired | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,408	1,442
Impaired | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,339	690
Impaired | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	236	244
Impaired | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 450	$ 670