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	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 21,103,946	$ 20,024,662
Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	20,172,372	18,864,595
Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	733,281	925,607
Performing Impaired (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	78,121	115,481
Nonperforming Impaired (Nonaccrual)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	120,172	118,979
Commercial Portfolio Segment | Software/internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	5,442,532	5,668,578
Commercial Portfolio Segment | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,131,181	1,189,114
Commercial Portfolio Segment | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	8,902,436	7,747,911
Commercial Portfolio Segment | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,748,313	1,866,685
Commercial Portfolio Segment | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	906,126	880,379
Commercial Portfolio Segment | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	572,188	505,222
Commercial Portfolio Segment | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	18,702,776	17,857,889
Commercial Portfolio Segment | Pass | Software/internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,922,821	4,924,923
Commercial Portfolio Segment | Pass | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	952,429	985,889
Commercial Portfolio Segment | Pass | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	8,896,099	7,747,317
Commercial Portfolio Segment | Pass | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,576,136	1,707,499
Commercial Portfolio Segment | Pass | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	888,305	865,354
Commercial Portfolio Segment | Pass | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	550,943	480,845
Commercial Portfolio Segment | Pass | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	17,786,733	16,711,827
Commercial Portfolio Segment | Performing (Criticized) | Software/internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	390,084	620,907
Commercial Portfolio Segment | Performing (Criticized) | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	148,732	137,830
Commercial Portfolio Segment | Performing (Criticized) | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	6,029	594
Commercial Portfolio Segment | Performing (Criticized) | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	140,706	120,825
Commercial Portfolio Segment | Performing (Criticized) | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	14,654	11,838
Commercial Portfolio Segment | Performing (Criticized) | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	20,837	23,510
Commercial Portfolio Segment | Performing (Criticized) | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	721,042	915,504
Commercial Portfolio Segment | Performing Impaired (Criticized) | Software/internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	42,413	46,143
Commercial Portfolio Segment | Performing Impaired (Criticized) | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	23,710	58,814
Commercial Portfolio Segment | Performing Impaired (Criticized) | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	308	0
Commercial Portfolio Segment | Performing Impaired (Criticized) | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	8,972	6,578
Commercial Portfolio Segment | Performing Impaired (Criticized) | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,718	2,696
Commercial Portfolio Segment | Performing Impaired (Criticized) | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	464
Commercial Portfolio Segment | Performing Impaired (Criticized) | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	78,121	114,695
Commercial Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Software/internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	87,214	76,605
Commercial Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	6,310	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	22,499	31,783
Commercial Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	449	491
Commercial Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	408	403
Commercial Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	116,880	115,863
Consumer Portfolio Segment | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,125,326	1,925,620
Consumer Portfolio Segment | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	275,844	241,153
Consumer Portfolio Segment | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,401,170	2,166,773
Consumer Portfolio Segment | Pass | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,112,234	1,914,512
Consumer Portfolio Segment | Pass | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	273,405	238,256
Consumer Portfolio Segment | Pass | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,385,639	2,152,768
Consumer Portfolio Segment | Performing (Criticized) | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	11,764	9,604
Consumer Portfolio Segment | Performing (Criticized) | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	475	499
Consumer Portfolio Segment | Performing (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	12,239	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	0	786
Consumer Portfolio Segment | Performing Impaired (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	786
Consumer Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,328	1,504
Consumer Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,964	1,612
Consumer Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 3,292	$ 3,116