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, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 32,346	$ 96,090
Current	16,824,785	14,392,676
Loans Past Due 90 Days or More Still Accruing Interest	0	1,302
Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	24,792	71,879
Current	16,649,655	14,378,750
Loans Past Due 90 Days or More Still Accruing Interest	0	1,302
Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	7,554	24,211
Current	175,130	13,926
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	10,800	68,292
30 - 59 Days Past Due | Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	10,467	67,694
30 - 59 Days Past Due | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	333	598
60 - 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	14,325	4,176
60 - 89 Days Past Due | Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	14,325	2,883
60 - 89 Days Past Due | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	1,293
Greater Than 90 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	7,221	23,622
Greater Than 90 Days Past Due | Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	1,302
Greater Than 90 Days Past Due | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	7,221	22,320
Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	18,673	68,696
Current	14,885,865	13,104,252
Loans Past Due 90 Days or More Still Accruing Interest	0	52
Commercial loans | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	10,022	12,668
Current	5,371,222	4,950,291
Loans Past Due 90 Days or More Still Accruing Interest	0	52
Commercial loans | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,127	13,550
Current	1,051,368	1,124,423
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial loans | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	17	40,773
Current	5,511,912	4,580,526
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	7,390	1,524
Current	1,665,801	1,298,728
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	81	0
Current	847,249	795,345
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	36	181
Current	438,313	354,939
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	5,328	66,102
Commercial loans | 30 - 59 Days Past Due | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,384	10,989
Commercial loans | 30 - 59 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,061	13,424
Commercial loans | 30 - 59 Days Past Due | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	40,773
Commercial loans | 30 - 59 Days Past Due | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	853	738
Commercial loans | 30 - 59 Days Past Due | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	16	0
Commercial loans | 30 - 59 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	14	178
Commercial loans | 60 - 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	13,345	2,542
Commercial loans | 60 - 89 Days Past Due | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	6,638	1,627
Commercial loans | 60 - 89 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	66	126
Commercial loans | 60 - 89 Days Past Due | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	17	0
Commercial loans | 60 - 89 Days Past Due | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	6,537	786
Commercial loans | 60 - 89 Days Past Due | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	65	0
Commercial loans | 60 - 89 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	22	3
Commercial loans | Greater Than 90 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	52
Commercial loans | Greater Than 90 Days Past Due | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	52
Commercial loans | Greater Than 90 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	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	6,119	3,183
Current	1,763,790	1,274,498
Loans Past Due 90 Days or More Still Accruing Interest	0	1,250
Consumer, Other | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	343	0
Current	226,369	160,212
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Consumer, Other | Real estate secured consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5,776	3,183
Current	1,537,421	1,114,286
Loans Past Due 90 Days or More Still Accruing Interest	0	1,250
Consumer, Other | 30 - 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5,139	1,592
Consumer, Other | 30 - 59 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	228	0
Consumer, Other | 30 - 59 Days Past Due | Real estate secured consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,911	1,592
Consumer, Other | 60 - 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	980	341
Consumer, Other | 60 - 89 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	115	0
Consumer, Other | 60 - 89 Days Past Due | Real estate secured consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	865	341
Consumer, Other | Greater Than 90 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	1,250
Consumer, Other | Greater Than 90 Days Past Due | Other
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	$ 1,250