Loans and Allowance for Loan Losses - Aging of Gross Loans, Broken out by Portfolio Segment and Class of Financing Receivable (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	$ 19,710	$ 68,292
60 - 89 Days Past Due	15,861	4,176
Greater Than 90 Days Past Due	25,019	23,622
Total Past Due	60,590	96,090
Current	14,486,155	14,392,676
Loans Past Due 90 Days or More Still Accruing Interest	3,099	1,302
Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	1,970	10,989
60 - 89 Days Past Due	162	1,627
Greater Than 90 Days Past Due	160	52
Total Past Due	2,292	12,668
Current	4,876,739	4,950,291
Loans Past Due 90 Days or More Still Accruing Interest	160	52
Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	298	13,424
60 - 89 Days Past Due	9,219	126
Greater Than 90 Days Past Due	0	0
Total Past Due	9,517	13,550
Current	1,066,598	1,124,423
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	11,462	40,773
60 - 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	11,462	40,773
Current	4,536,175	4,580,526
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Life science & healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	3,768	738
60 - 89 Days Past Due	0	786
Greater Than 90 Days Past Due	1,689	0
Total Past Due	5,457	1,524
Current	1,405,856	1,298,728
Loans Past Due 90 Days or More Still Accruing Interest	1,689	0
Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	0	0
60 - 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	0	0
Current	800,197	795,345
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	1,074	178
60 - 89 Days Past Due	0	3
Greater Than 90 Days Past Due	0	0
Total Past Due	1,074	181
Current	410,752	354,939
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	18,572	66,102
60 - 89 Days Past Due	9,381	2,542
Greater Than 90 Days Past Due	1,849	52
Total Past Due	29,802	68,696
Current	13,096,317	13,104,252
Loans Past Due 90 Days or More Still Accruing Interest	1,849	52
Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	415	1,592
60 - 89 Days Past Due	0	341
Greater Than 90 Days Past Due	1,250	1,250
Total Past Due	1,665	3,183
Current	1,206,762	1,114,286
Loans Past Due 90 Days or More Still Accruing Interest	1,250	1,250
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	410	0
60 - 89 Days Past Due	625	0
Greater Than 90 Days Past Due	0	0
Total Past Due	1,035	0
Current	168,782	160,212
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	825	1,592
60 - 89 Days Past Due	625	341
Greater Than 90 Days Past Due	1,250	1,250
Total Past Due	2,700	3,183
Current	1,375,544	1,274,498
Loans Past Due 90 Days or More Still Accruing Interest	1,250	1,250
Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	19,397	67,694
60 - 89 Days Past Due	10,006	2,883
Greater Than 90 Days Past Due	3,099	1,302
Total Past Due	32,502	71,879
Current	14,471,861	14,378,750
Loans Past Due 90 Days or More Still Accruing Interest	3,099	1,302
Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	313	598
60 - 89 Days Past Due	5,855	1,293
Greater Than 90 Days Past Due	21,920	22,320
Total Past Due	28,088	24,211
Current	14,294	13,926
Loans Past Due 90 Days or More Still Accruing Interest	$ 0	$ 0