Loans and Allowance for Loan Losses - Credit Quality Indicators, Broken out by Portfolio Segment and Class of Financing Receivables (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 14,370,930	$ 14,488,766
Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	13,499,057	13,729,421
Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	771,071	721,208
Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	100,802	38,137
Commercial Portfolio Segment | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	5,026,076	4,996,246
Commercial Portfolio Segment | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,058,436	1,140,494
Commercial Portfolio Segment | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,023,832	4,621,299
Commercial Portfolio Segment | Life science & healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,489,055	1,300,727
Commercial Portfolio Segment | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	825,369	796,649
Commercial Portfolio Segment | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	381,424	355,353
Commercial Portfolio Segment | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	12,804,192	13,210,768
Commercial Portfolio Segment | Pass | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,459,368	4,611,253
Commercial Portfolio Segment | Pass | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	920,574	945,998
Commercial Portfolio Segment | Pass | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,019,826	4,615,231
Commercial Portfolio Segment | Pass | Life science & healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,375,174	1,165,266
Commercial Portfolio Segment | Pass | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	806,346	774,962
Commercial Portfolio Segment | Pass | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	365,538	346,153
Commercial Portfolio Segment | Pass | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	11,946,826	12,458,863
Commercial Portfolio Segment | Performing (Criticized) | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	477,237	351,706
Commercial Portfolio Segment | Performing (Criticized) | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	135,505	191,975
Commercial Portfolio Segment | Performing (Criticized) | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,006	6,068
Commercial Portfolio Segment | Performing (Criticized) | Life science & healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	111,448	134,986
Commercial Portfolio Segment | Performing (Criticized) | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	17,787	20,383
Commercial Portfolio Segment | Performing (Criticized) | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	10,820	8,967
Commercial Portfolio Segment | Performing (Criticized) | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	756,803	714,085
Commercial Portfolio Segment | Impaired | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	89,471	33,287
Commercial Portfolio Segment | Impaired | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,357	2,521
Commercial Portfolio Segment | Impaired | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	0
Commercial Portfolio Segment | Impaired | Life science & healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,433	475
Commercial Portfolio Segment | Impaired | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,236	1,304
Commercial Portfolio Segment | Impaired | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	5,066	233
Commercial Portfolio Segment | Impaired | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	100,563	37,820
Consumer Portfolio Segment | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,340,106	1,117,661
Consumer Portfolio Segment | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	226,632	160,337
Consumer Portfolio Segment | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,566,738	1,277,998
Consumer Portfolio Segment | Pass | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,329,834	1,112,396
Consumer Portfolio Segment | Pass | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	222,397	158,162
Consumer Portfolio Segment | Pass | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,552,231	1,270,558
Consumer Portfolio Segment | Performing (Criticized) | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	10,100	5,073
Consumer Portfolio Segment | Performing (Criticized) | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,168	2,050
Consumer Portfolio Segment | Performing (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	14,268	7,123
Consumer Portfolio Segment | Impaired | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	172	192
Consumer Portfolio Segment | Impaired | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	67	125
Consumer Portfolio Segment | Impaired | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 239	$ 317