Loans and Allowance for Loan Losses - Aging of Gross Loans, Broken out by Portfolio Segment and Class of Financing Receivable (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 199,927	$ 98,292
Current	23,054,226	19,926,370
Loans Past Due 90 Days or More Still Accruing Interest	191	33
Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	156,278	49,025
Current	22,923,014	19,741,177
Loans Past Due 90 Days or More Still Accruing Interest	191	33
Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	43,649	49,267
Current	131,212	185,193
Loans Past Due 90 Days or More Still Accruing Interest	0	0
30 - 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	111,525	81,575
30 - 59 Days Past Due | Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	110,181	46,939
30 - 59 Days Past Due | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,344	34,636
60 - 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	57,808	5,504
60 - 89 Days Past Due | Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	45,906	2,053
60 - 89 Days Past Due | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	11,902	3,451
Equal to or Greater Than 90 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	30,594	11,213
Equal to or Greater Than 90 Days Past Due | Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	191	33
Equal to or Greater Than 90 Days Past Due | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	30,403	11,180
Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	152,786	46,773
Current	20,302,800	17,580,558
Loans Past Due 90 Days or More Still Accruing Interest	191	33
Commercial loans | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	20,924	38,255
Current	6,101,147	5,507,575
Loans Past Due 90 Days or More Still Accruing Interest	141	6
Commercial loans | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,272	5,654
Current	1,163,278	1,118,065
Loans Past Due 90 Days or More Still Accruing Interest	50	27
Commercial loans | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	125,146	689
Current	9,835,317	7,747,222
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial loans | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,581	834
Current	1,841,692	1,827,490
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial loans | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	418	1,007
Current	871,074	876,185
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	445	334
Current	490,292	504,021
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial loans | 30 - 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	107,221	44,687
Commercial loans | 30 - 59 Days Past Due | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	14,257	37,087
Commercial loans | 30 - 59 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,145	5,591
Commercial loans | 30 - 59 Days Past Due | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	86,566	689
Commercial loans | 30 - 59 Days Past Due | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,390	283
Commercial loans | 30 - 59 Days Past Due | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	418	1,003
Commercial loans | 30 - 59 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	445	34
Commercial loans | 60 - 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	45,374	2,053
Commercial loans | 60 - 89 Days Past Due | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	6,526	1,162
Commercial loans | 60 - 89 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	77	36
Commercial loans | 60 - 89 Days Past Due | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	38,580	0
Commercial loans | 60 - 89 Days Past Due | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	191	551
Commercial loans | 60 - 89 Days Past Due | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	4
Commercial loans | 60 - 89 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	300
Commercial loans | Equal to or Greater Than 90 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	191	33
Commercial loans | Equal to or Greater Than 90 Days Past Due | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	141	6
Commercial loans | Equal to or Greater Than 90 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	50	27
Commercial loans | Equal to or Greater Than 90 Days Past Due | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial loans | Equal to or Greater Than 90 Days Past Due | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial loans | Equal to or Greater Than 90 Days Past Due | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial loans | Equal to or Greater Than 90 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Consumer, Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,492	2,252
Current	2,620,214	2,160,619
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Consumer, Other | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	796	1,402
Consumer, Other | Real estate secured consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,696	850
Current	2,292,980	1,923,266
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Consumer, Other | Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	327,234	237,353
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Consumer, Other | 30 - 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,960	2,252
Consumer, Other | 30 - 59 Days Past Due | Real estate secured consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,164	850
Consumer, Other | 30 - 59 Days Past Due | Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	796	1,402
Consumer, Other | 60 - 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	532	0
Consumer, Other | 60 - 89 Days Past Due | Real estate secured consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	532	0
Consumer, Other | 60 - 89 Days Past Due | Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Consumer, Other | Equal to or Greater Than 90 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Consumer, Other | Equal to or Greater Than 90 Days Past Due | Real estate secured consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Consumer, Other | Equal to or Greater Than 90 Days Past Due | Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 0	$ 0