Loans and Allowance for Loan Losses - Credit Quality Indicators, Broken out by Portfolio Segment and Class of Financing Receivables (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 16,857,131	$ 14,488,766
Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	15,926,946	13,729,421
Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	747,501	721,208
Performing Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	59,292	0
Non Performing Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	123,392	38,137
Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	15,087,079	13,210,768
Commercial loans | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	5,482,110	4,996,246
Commercial loans | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,080,231	1,140,494
Commercial loans | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	5,511,929	4,621,299
Commercial loans | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,724,545	1,300,727
Commercial loans | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	849,395	796,649
Commercial loans | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	438,869	355,353
Commercial loans | Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	14,162,877	12,458,863
Commercial loans | Pass | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,933,179	4,611,253
Commercial loans | Pass | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	955,675	945,998
Commercial loans | Pass | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	5,474,929	4,615,231
Commercial loans | Pass | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,544,555	1,165,266
Commercial loans | Pass | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	825,058	774,962
Commercial loans | Pass | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	429,481	346,153
Commercial loans | Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	741,661	714,085
Commercial loans | Performing (Criticized) | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	448,065	351,706
Commercial loans | Performing (Criticized) | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	96,820	191,975
Commercial loans | Performing (Criticized) | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	37,000	6,068
Commercial loans | Performing (Criticized) | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	128,636	134,986
Commercial loans | Performing (Criticized) | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	22,272	20,383
Commercial loans | Performing (Criticized) | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	8,868	8,967
Commercial loans | Performing Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	59,292	0
Commercial loans | Performing Impaired | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	23,321	0
Commercial loans | Performing Impaired | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	27,306	0
Commercial loans | Performing Impaired | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	0
Commercial loans | Performing Impaired | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	7,247	0
Commercial loans | Performing Impaired | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	898	0
Commercial loans | Performing Impaired | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	520	0
Commercial loans | Non Performing Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	123,249	37,820
Commercial loans | Non Performing Impaired | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	77,545	33,287
Commercial loans | Non Performing Impaired | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	430	2,521
Commercial loans | Non Performing Impaired | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	0
Commercial loans | Non Performing Impaired | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	44,107	475
Commercial loans | Non Performing Impaired | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,167	1,304
Commercial loans | Non Performing Impaired | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	233
Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,770,052	1,277,998
Consumer loans | Real estate secured consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,543,340	1,117,661
Consumer loans | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	226,712	160,337
Consumer loans | Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,764,069	1,270,558
Consumer loans | Pass | Real estate secured consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,539,468	1,112,396
Consumer loans | Pass | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	224,601	158,162
Consumer loans | Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	5,840	7,123
Consumer loans | Performing (Criticized) | Real estate secured consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,729	5,073
Consumer loans | Performing (Criticized) | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,111	2,050
Consumer loans | Performing Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	0
Consumer loans | Performing Impaired | Real estate secured consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	0
Consumer loans | Performing Impaired | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	0
Consumer loans | Non Performing Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	143	317
Consumer loans | Non Performing Impaired | Real estate secured consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	143	192
Consumer loans | Non Performing Impaired | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 0	$ 125