Loans, Allowance for Loan Losses and Allowance for Unfunded Credit Commitments - Credit Quality Indicators, Broken out by Portfolio Segment and Class of Financing Receivables (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 20,548,651	$ 20,024,662
Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	19,475,269	18,864,595
Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	870,766	925,607
Performing Impaired (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	63,852	115,481
Nonperforming Impaired (Nonaccrual)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	138,764	118,979
Commercial Portfolio Segment | Software/internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	5,505,796	5,668,578
Commercial Portfolio Segment | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,108,735	1,189,114
Commercial Portfolio Segment | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	8,437,354	7,747,911
Commercial Portfolio Segment | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,783,037	1,866,685
Commercial Portfolio Segment | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	876,665	880,379
Commercial Portfolio Segment | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	595,639	505,222
Commercial Portfolio Segment | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	18,307,226	17,857,889
Commercial Portfolio Segment | Pass | Software/internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,858,104	4,924,923
Commercial Portfolio Segment | Pass | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	938,269	985,889
Commercial Portfolio Segment | Pass | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	8,436,841	7,747,317
Commercial Portfolio Segment | Pass | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,588,709	1,707,499
Commercial Portfolio Segment | Pass | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	854,409	865,354
Commercial Portfolio Segment | Pass | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	573,527	480,845
Commercial Portfolio Segment | Pass | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	17,249,859	16,711,827
Commercial Portfolio Segment | Performing (Criticized) | Software/internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	522,856	620,907
Commercial Portfolio Segment | Performing (Criticized) | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	140,933	137,830
Commercial Portfolio Segment | Performing (Criticized) | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	167	594
Commercial Portfolio Segment | Performing (Criticized) | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	155,035	120,825
Commercial Portfolio Segment | Performing (Criticized) | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	18,935	11,838
Commercial Portfolio Segment | Performing (Criticized) | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	20,453	23,510
Commercial Portfolio Segment | Performing (Criticized) | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	858,379	915,504
Commercial Portfolio Segment | Performing Impaired (Criticized) | Software/internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	25,165	46,143
Commercial Portfolio Segment | Performing Impaired (Criticized) | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	27,464	58,814
Commercial Portfolio Segment | Performing Impaired (Criticized) | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	346	0
Commercial Portfolio Segment | Performing Impaired (Criticized) | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	7,153	6,578
Commercial Portfolio Segment | Performing Impaired (Criticized) | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,831	2,696
Commercial Portfolio Segment | Performing Impaired (Criticized) | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	357	464
Commercial Portfolio Segment | Performing Impaired (Criticized) | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	63,316	114,695
Commercial Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Software/internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	99,671	76,605
Commercial Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,069	6,581
Commercial Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	0
Commercial Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	32,140	31,783
Commercial Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	490	491
Commercial Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,302	403
Commercial Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	135,672	115,863
Consumer Portfolio Segment | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,010,464	1,925,620
Consumer Portfolio Segment | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	230,961	241,153
Consumer Portfolio Segment | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,241,425	2,166,773
Consumer Portfolio Segment | Pass | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,997,248	1,914,512
Consumer Portfolio Segment | Pass | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	228,162	238,256
Consumer Portfolio Segment | Pass | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,225,410	2,152,768
Consumer Portfolio Segment | Performing (Criticized) | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	11,736	9,604
Consumer Portfolio Segment | Performing (Criticized) | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	651	499
Consumer Portfolio Segment | Performing (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	12,387	10,103
Consumer Portfolio Segment | Performing Impaired (Criticized) | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	0
Consumer Portfolio Segment | Performing Impaired (Criticized) | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	536	786
Consumer Portfolio Segment | Performing Impaired (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	536	786
Consumer Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,480	1,504
Consumer Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,612	1,612
Consumer Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 3,092	$ 3,116