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	Jun. 30, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	$ 12,524	$ 10,563
60 - 89 Days Past Due	11,715	10,063
Greater Than 90 Days Past Due	18,510	2,288
Total Past Due	42,749	22,914
Current	9,662,715	9,001,334
Loans Past Due 90 Days or More Still Accruing Interest	1,861	19
Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	12,499	6,551
60 - 89 Days Past Due	10,350	387
Greater Than 90 Days Past Due	1,861	19
Total Past Due	24,710	6,957
Current	8,778,961	8,151,780
Loans Past Due 90 Days or More Still Accruing Interest	1,861	19
Commercial loans | Software
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	765	5,890
60 - 89 Days Past Due	1,082	238
Greater Than 90 Days Past Due	727	19
Total Past Due	2,574	6,147
Current	3,584,748	3,284,489
Loans Past Due 90 Days or More Still Accruing Interest	727	19
Commercial loans | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	7,493	167
60 - 89 Days Past Due	56	32
Greater Than 90 Days Past Due	0	0
Total Past Due	7,549	199
Current	1,185,481	1,107,422
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial loans | Venture capital/private equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	3,311	7
60 - 89 Days Past Due	4,670	0
Greater Than 90 Days Past Due	0	0
Total Past Due	7,981	7
Current	1,934,594	1,749,896
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial loans | Life science
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	185	207
60 - 89 Days Past Due	415	117
Greater Than 90 Days Past Due	722	0
Total Past Due	1,322	324
Current	1,094,259	1,076,468
Loans Past Due 90 Days or More Still Accruing Interest	722	0
Commercial loans | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	636	0
60 - 89 Days Past Due	4,035	0
Greater Than 90 Days Past Due	0	0
Total Past Due	4,671	0
Current	604,873	554,886
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	109	280
60 - 89 Days Past Due	92	0
Greater Than 90 Days Past Due	412	0
Total Past Due	613	280
Current	375,006	378,619
Loans Past Due 90 Days or More Still Accruing Interest	412	0
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	25	111
60 - 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	25	111
Current	860,609	827,121
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Consumer loans | Real estate secured loans
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	774,692	683,254
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Consumer loans | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	25	111
60 - 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	25	111
Current	85,917	143,867
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	12,524	6,662
60 - 89 Days Past Due	10,350	387
Greater Than 90 Days Past Due	1,861	19
Total Past Due	24,735	7,068
Current	9,639,570	8,978,901
Loans Past Due 90 Days or More Still Accruing Interest	1,861	19
Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	0	3,901
60 - 89 Days Past Due	1,365	9,676
Greater Than 90 Days Past Due	16,649	2,269
Total Past Due	18,014	15,846
Current	23,145	22,433
Loans Past Due 90 Days or More Still Accruing Interest	$ 0	$ 0