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	Mar. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 130,354	$ 98,292
Current	20,418,297	19,926,370
Loans Past Due 90 Days or More Still Accruing Interest	60	33
Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	84,906	49,025
Current	20,261,129	19,741,177
Loans Past Due 90 Days or More Still Accruing Interest	60	33
Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	45,448	49,267
Current	157,168	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	81,643	81,575
30 - 59 Days Past Due | Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	76,755	46,939
30 - 59 Days Past Due | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,888	34,636
60 - 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	10,298	5,504
60 - 89 Days Past Due | Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	8,091	2,053
60 - 89 Days Past Due | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,207	3,451
Greater Than 90 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	38,413	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	60	33
Greater Than 90 Days Past Due | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	38,353	11,180
Commercial Portfolio Segment | Software/internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	30,296	38,255
Current	5,350,664	5,507,575
Loans Past Due 90 Days or More Still Accruing Interest	38	6
Commercial Portfolio Segment | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	7,430	5,654
Current	1,071,772	1,118,065
Loans Past Due 90 Days or More Still Accruing Interest	20	27
Commercial Portfolio Segment | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	37,113	689
Current	8,399,895	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	730	834
Current	1,743,014	1,827,490
Loans Past Due 90 Days or More Still Accruing Interest	2	0
Commercial Portfolio Segment | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,238	1,007
Current	869,106	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	1,984	334
Current	591,996	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	81,791	46,773
Current	18,026,447	17,580,558
Loans Past Due 90 Days or More Still Accruing Interest	60	33
Commercial Portfolio Segment | 30 - 59 Days Past Due | Software/internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	26,927	37,087
Commercial Portfolio Segment | 30 - 59 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	7,406	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	33,878	689
Commercial Portfolio Segment | 30 - 59 Days Past Due | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	708	283
Commercial Portfolio Segment | 30 - 59 Days Past Due | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,037	1,003
Commercial Portfolio Segment | 30 - 59 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,684	34
Commercial Portfolio Segment | 30 - 59 Days Past Due | Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	73,640	44,687
Commercial Portfolio Segment | 60 - 89 Days Past Due | Software/internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,331	1,162
Commercial Portfolio Segment | 60 - 89 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4	36
Commercial Portfolio Segment | 60 - 89 Days Past Due | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,235	0
Commercial Portfolio Segment | 60 - 89 Days Past Due | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	20	551
Commercial Portfolio Segment | 60 - 89 Days Past Due | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,201	4
Commercial Portfolio Segment | 60 - 89 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	300	300
Commercial Portfolio Segment | 60 - 89 Days Past Due | Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	8,091	2,053
Commercial Portfolio Segment | Greater Than 90 Days Past Due | Software/internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	38	6
Commercial Portfolio Segment | Greater Than 90 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	20	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	2	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	60	33
Consumer Portfolio Segment | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,115	850
Current	2,005,869	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	0	1,402
Current	228,813	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	3,115	2,252
Current	2,234,682	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	3,115	850
Consumer Portfolio Segment | 30 - 59 Days Past Due | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	1,402
Consumer Portfolio Segment | 30 - 59 Days Past Due | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,115	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	0	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	0	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