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, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 20,024,662	$ 16,857,131
Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	18,864,595	15,926,946
Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	925,607	747,501
Performing Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	115,481	59,292
Non Performing Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	118,979	123,392
Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	17,857,889	15,087,079
Commercial loans | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	5,668,578	5,482,110
Commercial loans | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,189,114	1,080,231
Commercial loans | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	7,747,911	5,511,929
Commercial loans | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,866,685	1,724,545
Commercial loans | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	880,379	849,395
Commercial loans | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	505,222	438,869
Commercial loans | Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	16,711,827	14,162,877
Commercial loans | Pass | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,924,923	4,933,179
Commercial loans | Pass | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	985,889	955,675
Commercial loans | Pass | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	7,747,317	5,474,929
Commercial loans | Pass | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,707,499	1,544,555
Commercial loans | Pass | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	865,354	825,058
Commercial loans | Pass | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	480,845	429,481
Commercial loans | Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	915,504	741,661
Commercial loans | Performing (Criticized) | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	620,907	448,065
Commercial loans | Performing (Criticized) | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	137,830	96,820
Commercial loans | Performing (Criticized) | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	594	37,000
Commercial loans | Performing (Criticized) | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	120,825	128,636
Commercial loans | Performing (Criticized) | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	11,838	22,272
Commercial loans | Performing (Criticized) | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	23,510	8,868
Commercial loans | Performing Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	114,695	59,292
Commercial loans | Performing Impaired | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	46,143	23,321
Commercial loans | Performing Impaired | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	58,814	27,306
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	6,578	7,247
Commercial loans | Performing Impaired | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,696	898
Commercial loans | Performing Impaired | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	464	520
Commercial loans | Non Performing Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	115,863	123,249
Commercial loans | Non Performing Impaired | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	76,605	77,545
Commercial loans | Non Performing Impaired | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	6,581	430
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	31,783	44,107
Commercial loans | Non Performing Impaired | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	491	1,167
Commercial loans | Non Performing Impaired | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	403	0
Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,166,773	1,770,052
Consumer loans | Real estate secured consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,925,620	1,543,340
Consumer loans | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	241,153	226,712
Consumer loans | Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,152,768	1,764,069
Consumer loans | Pass | Real estate secured consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,914,512	1,539,468
Consumer loans | Pass | Other Loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	238,256	224,601
Consumer loans | Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	10,103	5,840
Consumer loans | Performing (Criticized) | Real estate secured consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	9,604	3,729
Consumer loans | Performing (Criticized) | Other Loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	499	2,111
Consumer loans | Performing Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	786	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 Loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	786	0
Consumer loans | Non Performing Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,116	143
Consumer loans | Non Performing Impaired | Real estate secured consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,504	143
Consumer loans | Non Performing Impaired | Other Loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 1,612	$ 0