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, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 98,292	$ 32,346
Current	19,926,370	16,824,785
Loans Past Due 90 Days or More Still Accruing Interest	33	0
Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	49,025	24,792
Current	19,741,177	16,649,655
Loans Past Due 90 Days or More Still Accruing Interest	33	0
Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	49,267	7,554
Current	185,193	175,130
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	81,575	10,800
30 - 59 Days Past Due | Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	46,939	10,467
30 - 59 Days Past Due | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	34,636	333
60 - 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5,504	14,325
60 - 89 Days Past Due | Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,053	14,325
60 - 89 Days Past Due | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,451	0
Greater Than 90 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	11,213	7,221
Greater Than 90 Days Past Due | Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	33	0
Greater Than 90 Days Past Due | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	11,180	7,221
Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	46,773	18,673
Current	17,580,558	14,885,865
Loans Past Due 90 Days or More Still Accruing Interest	33	0
Commercial loans | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	38,255	10,022
Current	5,507,575	5,371,222
Loans Past Due 90 Days or More Still Accruing Interest	6	0
Commercial loans | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5,654	1,127
Current	1,118,065	1,051,368
Loans Past Due 90 Days or More Still Accruing Interest	27	0
Commercial loans | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	689	17
Current	7,747,222	5,511,912
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	834	7,390
Current	1,827,490	1,665,801
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	1,007	81
Current	876,185	847,249
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	334	36
Current	504,021	438,313
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	44,687	5,328
Commercial loans | 30 - 59 Days Past Due | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	37,087	3,384
Commercial loans | 30 - 59 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5,591	1,061
Commercial loans | 30 - 59 Days Past Due | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	689	0
Commercial loans | 30 - 59 Days Past Due | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	283	853
Commercial loans | 30 - 59 Days Past Due | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,003	16
Commercial loans | 30 - 59 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	34	14
Commercial loans | 60 - 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,053	13,345
Commercial loans | 60 - 89 Days Past Due | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,162	6,638
Commercial loans | 60 - 89 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	36	66
Commercial loans | 60 - 89 Days Past Due | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	17
Commercial loans | 60 - 89 Days Past Due | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	551	6,537
Commercial loans | 60 - 89 Days Past Due | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4	65
Commercial loans | 60 - 89 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	300	22
Commercial loans | Greater Than 90 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	33	0
Commercial loans | Greater Than 90 Days Past Due | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	6	0
Commercial loans | Greater Than 90 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	27	0
Commercial loans | 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 | Greater Than 90 Days Past Due | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial loans | Greater Than 90 Days Past Due | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial loans | 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	2,252	6,119
Current	2,160,619	1,763,790
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	1,402	343
Consumer, Other | Real estate secured consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	850	5,776
Current	1,923,266	1,537,421
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	237,353	226,369
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	2,252	5,139
Consumer, Other | 30 - 59 Days Past Due | Real estate secured consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	850	4,911
Consumer, Other | 30 - 59 Days Past Due | Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,402	228
Consumer, Other | 60 - 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	980
Consumer, Other | 60 - 89 Days Past Due | Real estate secured consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	865
Consumer, Other | 60 - 89 Days Past Due | Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	115
Consumer, Other | Greater Than 90 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Consumer, Other | 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 | Greater Than 90 Days Past Due | Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 0	$ 0