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, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 26,160,782	$ 23,254,153
Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	25,080,105	22,357,492
Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	902,498	721,800
Performing Impaired (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	53,337	55,602
Nonperforming Impaired (Nonaccrual)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	124,842	119,259
Commercial loans | Software/internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	6,291,788	6,232,725
Commercial loans | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,281,433	1,200,900
Commercial loans | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	12,233,005	9,961,121
Commercial loans | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,158,336	1,867,960
Commercial loans | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	885,050	874,369
Commercial loans | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	436,023	490,769
Commercial loans | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	23,285,635	20,627,844
Commercial loans | Pass | Software/internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	5,645,661	5,655,739
Commercial loans | Pass | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,163,629	1,112,574
Commercial loans | Pass | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	12,229,454	9,955,082
Commercial loans | Pass | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,909,151	1,720,613
Commercial loans | Pass | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	840,649	834,537
Commercial loans | Pass | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	432,652	469,721
Commercial loans | Pass | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	22,221,196	19,748,266
Commercial loans | Performing (Criticized) | Software/internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	543,607	466,332
Commercial loans | Performing (Criticized) | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	75,510	51,976
Commercial loans | Performing (Criticized) | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,551	5,381
Commercial loans | Performing (Criticized) | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	222,765	125,660
Commercial loans | Performing (Criticized) | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	41,877	36,955
Commercial loans | Performing (Criticized) | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,363	21,016
Commercial loans | Performing (Criticized) | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	890,673	707,320
Commercial loans | Performing Impaired (Criticized) | Software/internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	25,369	31,794
Commercial loans | Performing Impaired (Criticized) | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	25,201	20,165
Commercial loans | Performing Impaired (Criticized) | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	0
Commercial loans | Performing Impaired (Criticized) | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	250	1,167
Commercial loans | Performing Impaired (Criticized) | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,193	2,476
Commercial loans | Performing Impaired (Criticized) | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	0
Commercial loans | Performing Impaired (Criticized) | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	53,013	55,602
Commercial loans | Nonperforming Impaired (Nonaccrual) | Software/internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	77,151	78,860
Commercial loans | Nonperforming Impaired (Nonaccrual) | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	17,093	16,185
Commercial loans | Nonperforming Impaired (Nonaccrual) | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	658
Commercial loans | Nonperforming Impaired (Nonaccrual) | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	26,170	20,520
Commercial loans | Nonperforming Impaired (Nonaccrual) | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	331	401
Commercial loans | Nonperforming Impaired (Nonaccrual) | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	8	32
Commercial loans | Nonperforming Impaired (Nonaccrual) | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	120,753	116,656
Consumer loans | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,477,871	2,297,857
Consumer loans | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	397,276	328,452
Consumer loans | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,875,147	2,626,309
Consumer loans | Pass | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,462,007	2,282,375
Consumer loans | Pass | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	396,902	326,851
Consumer loans | Pass | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,858,909	2,609,226
Consumer loans | Performing (Criticized) | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	11,451	13,301
Consumer loans | Performing (Criticized) | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	374	1,179
Consumer loans | Performing (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	11,825	14,480
Consumer loans | Performing Impaired (Criticized) | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	324	0
Consumer loans | Performing Impaired (Criticized) | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	0
Consumer loans | Performing Impaired (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	324	0
Consumer loans | Nonperforming Impaired (Nonaccrual) | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,089	2,181
Consumer loans | Nonperforming Impaired (Nonaccrual) | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	422
Consumer loans | Nonperforming Impaired (Nonaccrual) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 4,089	$ 2,603