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	Sep. 30, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 12,112,474	$ 10,995,268
Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,545,324	4,141,358
Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,082,090	1,224,480
Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,948,335	2,408,426
Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,257,130	1,181,266
Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	752,070	667,197
Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	354,773	399,828
Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	10,939,722	10,022,555
Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,047,487	873,070
Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	125,265	99,643
Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,172,752	972,713
Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	11,327,282	10,371,201
Pass | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,179,638	3,875,043
Pass | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	885,407	995,055
Pass | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,932,711	2,408,386
Pass | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,093,451	1,091,993
Pass | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	732,605	652,747
Pass | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	338,187	383,602
Pass | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	10,161,999	9,406,826
Pass | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,042,547	868,789
Pass | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	122,736	95,586
Pass | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,165,283	964,375
Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	773,505	572,418
Performing (Criticized) | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	356,956	238,697
Performing (Criticized) | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	196,683	209,758
Performing (Criticized) | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	15,624	0
Performing (Criticized) | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	162,679	87,995
Performing (Criticized) | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	18,126	13,008
Performing (Criticized) | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	16,400	15,536
Performing (Criticized) | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	766,468	564,994
Performing (Criticized) | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,732	4,037
Performing (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,305	3,387
Performing (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	7,037	7,424
Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	11,687	51,649
Impaired | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	8,730	27,618
Impaired | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	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	1,000	1,278
Impaired | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,339	1,442
Impaired | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	186	690
Impaired | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	11,255	50,735
Impaired | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	208	244
Impaired | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	224	670
Impaired | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 432	$ 914