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	Jun. 30, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 11,437,300	$ 10,995,268
Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	10,331,287	10,022,555
Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,106,013	972,713
Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,250,824	4,141,358
Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,154,639	1,224,480
Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,670,600	2,408,426
Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,176,928	1,181,266
Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	724,115	667,197
Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	354,181	399,828
Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	984,197	873,070
Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	121,816	99,643
Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	10,809,919	10,371,201
Pass | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	9,711,034	9,406,826
Pass | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,098,885	964,375
Pass | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,956,825	3,875,043
Pass | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	972,454	995,055
Pass | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,668,213	2,408,386
Pass | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,066,046	1,091,993
Pass | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	713,329	652,747
Pass | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	334,167	383,602
Pass | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	980,226	868,789
Pass | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	118,659	95,586
Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	605,035	572,418
Performing (Criticized) | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	598,463	564,994
Performing (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	6,572	7,424
Performing (Criticized) | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	279,583	238,697
Performing (Criticized) | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	176,683	209,758
Performing (Criticized) | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,387	0
Performing (Criticized) | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	110,882	87,995
Performing (Criticized) | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	9,413	13,008
Performing (Criticized) | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	19,515	15,536
Performing (Criticized) | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,751	4,037
Performing (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,821	3,387
Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	22,346	51,649
Impaired | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	21,790	50,735
Impaired | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	556	914
Impaired | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	14,416	27,618
Impaired | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	5,502	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	0	1,278
Impaired | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,373	1,442
Impaired | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	499	690
Impaired | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	220	244
Impaired | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 336	$ 670