Loans and Allowance for Loan Losses - Aging of Gross Loans, Broken out by Portfolio Segment and Class of Financing Receivable (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 48,589	$ 96,090
Current	14,322,341	14,392,676
Loans Past Due 90 Days or More Still Accruing Interest	47	1,302
Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	21,064	71,879
Current	14,249,064	14,378,750
Loans Past Due 90 Days or More Still Accruing Interest	47	1,302
Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	27,525	24,211
Current	73,277	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	34,864	68,292
30 - 59 Days Past Due | Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	7,339	67,694
30 - 59 Days Past Due | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	27,525	598
60 - 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	13,678	4,176
60 - 89 Days Past Due | Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	13,678	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	47	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	47	1,302
Greater Than 90 Days Past Due | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	22,320
Commercial Portfolio Segment | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	13,652	12,668
Current	4,922,953	4,950,291
Loans Past Due 90 Days or More Still Accruing Interest	47	52
Commercial Portfolio Segment | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,081	13,550
Current	1,051,998	1,124,423
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial Portfolio Segment | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	18	40,773
Current	4,023,814	4,580,526
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	1,031	1,524
Current	1,485,591	1,298,728
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	1,949	0
Current	822,184	795,345
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	38	181
Current	376,320	354,939
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	20,769	68,696
Current	12,682,860	13,104,252
Loans Past Due 90 Days or More Still Accruing Interest	47	52
Commercial Portfolio Segment | 30 - 59 Days Past Due | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	6,012	10,989
Commercial Portfolio Segment | 30 - 59 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	764	13,424
Commercial Portfolio Segment | 30 - 59 Days Past Due | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	18	40,773
Commercial Portfolio Segment | 30 - 59 Days Past Due | Life science & healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	379	738
Commercial Portfolio Segment | 30 - 59 Days Past Due | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	150	0
Commercial Portfolio Segment | 30 - 59 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	178
Commercial Portfolio Segment | 30 - 59 Days Past Due | Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	7,323	66,102
Commercial Portfolio Segment | 60 - 89 Days Past Due | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	7,593	1,627
Commercial Portfolio Segment | 60 - 89 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,317	126
Commercial Portfolio Segment | 60 - 89 Days Past Due | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial Portfolio Segment | 60 - 89 Days Past Due | Life science & healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	652	786
Commercial Portfolio Segment | 60 - 89 Days Past Due | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,799	0
Commercial Portfolio Segment | 60 - 89 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	38	3
Commercial Portfolio Segment | 60 - 89 Days Past Due | Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	13,399	2,542
Commercial Portfolio Segment | Greater Than 90 Days Past Due | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	47	52
Commercial Portfolio Segment | Greater Than 90 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
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	47	52
Consumer Portfolio Segment | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	279	3,183
Current	1,339,655	1,114,286
Loans Past Due 90 Days or More Still Accruing Interest	0	1,250
Consumer Portfolio Segment | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	16	0
Current	226,549	160,212
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	295	3,183
Current	1,566,204	1,274,498
Loans Past Due 90 Days or More Still Accruing Interest	0	1,250
Consumer Portfolio Segment | 30 - 59 Days Past Due | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	1,592
Consumer Portfolio Segment | 30 - 59 Days Past Due | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	16	0
Consumer Portfolio Segment | 30 - 59 Days Past Due | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	16	1,592
Consumer Portfolio Segment | 60 - 89 Days Past Due | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	279	341
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	279	341
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	1,250
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	$ 1,250