Loans and Allowance for Loan Losses - Credit Quality Indicators, Broken out by Portfolio Segment and Class of Financing Receivables (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 15,429,941	$ 14,488,766
Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	14,562,676	13,729,421
Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	751,804	721,208
Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	115,461	38,137
Commercial Portfolio Segment | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	5,320,056	4,996,246
Commercial Portfolio Segment | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	970,915	1,140,494
Commercial Portfolio Segment | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,611,953	4,621,299
Commercial Portfolio Segment | Life science & healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,612,680	1,300,727
Commercial Portfolio Segment | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	829,205	796,649
Commercial Portfolio Segment | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	429,310	355,353
Commercial Portfolio Segment | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	13,774,119	13,210,768
Commercial Portfolio Segment | Pass | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,802,522	4,611,253
Commercial Portfolio Segment | Pass | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	834,067	945,998
Commercial Portfolio Segment | Pass | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,611,953	4,615,231
Commercial Portfolio Segment | Pass | Life science & healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,446,972	1,165,266
Commercial Portfolio Segment | Pass | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	804,411	774,962
Commercial Portfolio Segment | Pass | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	417,459	346,153
Commercial Portfolio Segment | Pass | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	12,917,384	12,458,863
Commercial Portfolio Segment | Performing (Criticized) | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	452,742	351,706
Commercial Portfolio Segment | Performing (Criticized) | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	133,085	191,975
Commercial Portfolio Segment | Performing (Criticized) | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	6,068
Commercial Portfolio Segment | Performing (Criticized) | Life science & healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	120,319	134,986
Commercial Portfolio Segment | Performing (Criticized) | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	23,593	20,383
Commercial Portfolio Segment | Performing (Criticized) | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	11,694	8,967
Commercial Portfolio Segment | Performing (Criticized) | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	741,433	714,085
Commercial Portfolio Segment | Impaired | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	64,792	33,287
Commercial Portfolio Segment | Impaired | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,763	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	45,389	475
Commercial Portfolio Segment | Impaired | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,201	1,304
Commercial Portfolio Segment | Impaired | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	157	233
Commercial Portfolio Segment | Impaired | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	115,302	37,820
Consumer Portfolio Segment | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,443,170	1,117,661
Consumer Portfolio Segment | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	212,652	160,337
Consumer Portfolio Segment | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,655,822	1,277,998
Consumer Portfolio Segment | Pass | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,433,926	1,112,396
Consumer Portfolio Segment | Pass | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	211,366	158,162
Consumer Portfolio Segment | Pass | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,645,292	1,270,558
Consumer Portfolio Segment | Performing (Criticized) | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	9,085	5,073
Consumer Portfolio Segment | Performing (Criticized) | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,286	2,050
Consumer Portfolio Segment | Performing (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	10,371	7,123
Consumer Portfolio Segment | Impaired | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	159	192
Consumer Portfolio Segment | Impaired | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	125
Consumer Portfolio Segment | Impaired | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 159	$ 317