Loans, Allowance for Loan Losses and Allowance for Unfunded Credit Commitments - Aging of Gross Loans, Broken out by Portfolio Segment and Class of Financing Receivable (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 180,576	$ 98,292
Current	22,149,253	19,926,370
Loans Past Due 90 Days or More Still Accruing Interest	764	33
Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	153,218	49,025
Current	21,983,139	19,741,177
Loans Past Due 90 Days or More Still Accruing Interest	764	33
Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	27,358	49,267
Current	166,114	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	113,207	81,575
30 - 59 Days Past Due | Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	112,616	46,939
30 - 59 Days Past Due | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	591	34,636
60 - 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	40,149	5,504
60 - 89 Days Past Due | Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	39,838	2,053
60 - 89 Days Past Due | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	311	3,451
Greater Than 90 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	27,220	11,213
Greater Than 90 Days Past Due | Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	764	33
Greater Than 90 Days Past Due | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	26,456	11,180
Commercial Portfolio Segment | Software/internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	49,806	38,255
Current	5,686,655	5,507,575
Loans Past Due 90 Days or More Still Accruing Interest	138	6
Commercial Portfolio Segment | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	943	5,654
Current	1,080,341	1,118,065
Loans Past Due 90 Days or More Still Accruing Interest	626	27
Commercial Portfolio Segment | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	69,997	689
Current	9,563,613	7,747,222
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial Portfolio Segment | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	20,956	834
Current	1,729,909	1,827,490
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial Portfolio Segment | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,161	1,007
Current	916,451	876,185
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial Portfolio Segment | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	217	334
Current	512,891	504,021
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial Portfolio Segment | Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	146,080	46,773
Current	19,489,860	17,580,558
Loans Past Due 90 Days or More Still Accruing Interest	764	33
Commercial Portfolio Segment | 30 - 59 Days Past Due | Software/internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	45,943	37,087
Commercial Portfolio Segment | 30 - 59 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	273	5,591
Commercial Portfolio Segment | 30 - 59 Days Past Due | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	35,628	689
Commercial Portfolio Segment | 30 - 59 Days Past Due | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	20,956	283
Commercial Portfolio Segment | 30 - 59 Days Past Due | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,521	1,003
Commercial Portfolio Segment | 30 - 59 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	7	34
Commercial Portfolio Segment | 30 - 59 Days Past Due | Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	106,328	44,687
Commercial Portfolio Segment | 60 - 89 Days Past Due | Software/internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,725	1,162
Commercial Portfolio Segment | 60 - 89 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	44	36
Commercial Portfolio Segment | 60 - 89 Days Past Due | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	34,369	0
Commercial Portfolio Segment | 60 - 89 Days Past Due | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	551
Commercial Portfolio Segment | 60 - 89 Days Past Due | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	640	4
Commercial Portfolio Segment | 60 - 89 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	210	300
Commercial Portfolio Segment | 60 - 89 Days Past Due | Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	38,988	2,053
Commercial Portfolio Segment | Greater Than 90 Days Past Due | Software/internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	138	6
Commercial Portfolio Segment | Greater Than 90 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	626	27
Commercial Portfolio Segment | Greater Than 90 Days Past Due | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial Portfolio Segment | Greater Than 90 Days Past Due | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial Portfolio Segment | Greater Than 90 Days Past Due | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial Portfolio Segment | Greater Than 90 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial Portfolio Segment | Greater Than 90 Days Past Due | Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	764	33
Consumer Portfolio Segment | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,598	850
Current	2,199,978	1,923,266
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Consumer Portfolio Segment | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,540	1,402
Current	293,301	237,353
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Consumer Portfolio Segment | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	7,138	2,252
Current	2,493,279	2,160,619
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Consumer Portfolio Segment | 30 - 59 Days Past Due | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,748	850
Consumer Portfolio Segment | 30 - 59 Days Past Due | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,540	1,402
Consumer Portfolio Segment | 30 - 59 Days Past Due | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	6,288	2,252
Consumer Portfolio Segment | 60 - 89 Days Past Due | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	850	0
Consumer Portfolio Segment | 60 - 89 Days Past Due | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Consumer Portfolio Segment | 60 - 89 Days Past Due | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	850	0
Consumer Portfolio Segment | Greater Than 90 Days Past Due | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Consumer Portfolio Segment | Greater Than 90 Days Past Due | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Consumer Portfolio Segment | Greater Than 90 Days Past Due | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 0	$ 0