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, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 14,546,745	$ 14,488,766
Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,913,747	4,996,246
Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,076,625	1,140,494
Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,547,637	4,621,299
Life science & healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,411,563	1,300,727
Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	801,467	796,649
Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	417,182	355,353
Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	13,168,221	13,210,768
Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,208,637	1,117,661
Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	169,887	160,337
Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,378,524	1,277,998
Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	13,734,381	13,729,421
Pass | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,483,199	4,611,253
Pass | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	874,295	945,998
Pass | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,543,600	4,615,231
Pass | Life science & healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,282,275	1,165,266
Pass | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	780,710	774,962
Pass | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	404,481	346,153
Pass | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	12,368,560	12,458,863
Pass | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,199,907	1,112,396
Pass | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	165,914	158,162
Pass | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,365,821	1,270,558
Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	769,982	721,208
Performing (Criticized) | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	395,832	351,706
Performing (Criticized) | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	201,820	191,975
Performing (Criticized) | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,037	6,068
Performing (Criticized) | Life science & healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	129,038	134,986
Performing (Criticized) | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	19,487	20,383
Performing (Criticized) | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	7,345	8,967
Performing (Criticized) | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	757,559	714,085
Performing (Criticized) | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	8,520	5,073
Performing (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,903	2,050
Performing (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	12,423	7,123
Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	42,382	38,137
Impaired | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	34,716	33,287
Impaired | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	510	2,521
Impaired | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	0
Impaired | Life science & healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	250	475
Impaired | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,270	1,304
Impaired | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	5,356	233
Impaired | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	42,102	37,820
Impaired | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	210	192
Impaired | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	70	125
Impaired | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 280	$ 317