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, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 23,254,153	$ 20,024,662
Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	22,357,492	18,864,595
Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	721,800	925,607
Performing Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	55,602	115,481
Non Performing Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	119,259	118,979
Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	20,627,844	17,857,889
Commercial loans | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	6,232,725	5,668,578
Commercial loans | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,200,900	1,189,114
Commercial loans | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	9,961,121	7,747,911
Commercial loans | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,867,960	1,866,685
Commercial loans | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	874,369	880,379
Commercial loans | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	490,769	505,222
Commercial loans | Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	19,748,266	16,711,827
Commercial loans | Pass | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	5,655,739	4,924,923
Commercial loans | Pass | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,112,574	985,889
Commercial loans | Pass | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	9,955,082	7,747,317
Commercial loans | Pass | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,720,613	1,707,499
Commercial loans | Pass | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	834,537	865,354
Commercial loans | Pass | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	469,721	480,845
Commercial loans | Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	707,320	915,504
Commercial loans | Performing (Criticized) | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	466,332	620,907
Commercial loans | Performing (Criticized) | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	51,976	137,830
Commercial loans | Performing (Criticized) | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	5,381	594
Commercial loans | Performing (Criticized) | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	125,660	120,825
Commercial loans | Performing (Criticized) | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	36,955	11,838
Commercial loans | Performing (Criticized) | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	21,016	23,510
Commercial loans | Performing Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	55,602	114,695
Commercial loans | Performing Impaired | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	31,794	46,143
Commercial loans | Performing Impaired | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	20,165	58,814
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	1,167	6,578
Commercial loans | Performing Impaired | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,476	2,696
Commercial loans | Performing Impaired | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	464
Commercial loans | Non Performing Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	116,656	115,863
Commercial loans | Non Performing Impaired | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	78,860	76,605
Commercial loans | Non Performing Impaired | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	16,185	6,581
Commercial loans | Non Performing Impaired | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	658	0
Commercial loans | Non Performing Impaired | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	20,520	31,783
Commercial loans | Non Performing Impaired | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	401	491
Commercial loans | Non Performing Impaired | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	32	403
Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,626,309	2,166,773
Consumer loans | Real estate secured consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,297,857	1,925,620
Consumer loans | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	328,452	241,153
Consumer loans | Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,609,226	2,152,768
Consumer loans | Pass | Real estate secured consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,282,375	1,914,512
Consumer loans | Pass | Other Loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	326,851	238,256
Consumer loans | Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	14,480	10,103
Consumer loans | Performing (Criticized) | Real estate secured consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	13,301	9,604
Consumer loans | Performing (Criticized) | Other Loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,179	499
Consumer loans | Performing Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	786
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	0	786
Consumer loans | Non Performing Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,603	3,116
Consumer loans | Non Performing Impaired | Real estate secured consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	2,181	1,504
Consumer loans | Non Performing Impaired | Other Loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 422	$ 1,612