Loans and Allowance for Loan Losses - Allowance for Loan Losses Individually and Collectively Evaluated for Impairment (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	$ 4,681	$ 21,277
Financing Receivable, Individually Evaluated for Impairment	22,346	51,648
Recorded investment in loans	116,047	121,609
Financing Receivable, Collectively Evaluated for Impairment	11,326,365	10,854,738
Commercial loans
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	4,540	21,109
Financing Receivable, Individually Evaluated for Impairment	21,790	50,733
Recorded investment in loans	109,844	115,433
Financing Receivable, Collectively Evaluated for Impairment	10,220,375	9,882,687
Consumer loans
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	141	168
Financing Receivable, Individually Evaluated for Impairment	556	915
Recorded investment in loans	6,203	6,176
Financing Receivable, Collectively Evaluated for Impairment	1,105,990	972,051
Software
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	2,979	11,261
Financing Receivable, Individually Evaluated for Impairment	14,416	27,617
Recorded investment in loans	50,260	52,823
Financing Receivable, Collectively Evaluated for Impairment	4,197,774	4,075,019
Hardware
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	1,443	9,673
Financing Receivable, Individually Evaluated for Impairment	5,502	19,667
Recorded investment in loans	23,337	26,880
Financing Receivable, Collectively Evaluated for Impairment	1,138,642	1,193,365
Venture capital/private equity
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	0	19
Financing Receivable, Individually Evaluated for Impairment	0	39
Recorded investment in loans	19,004	16,366
Financing Receivable, Collectively Evaluated for Impairment	2,646,397	2,386,015
Life science
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	0	0
Financing Receivable, Individually Evaluated for Impairment	0	1,278
Recorded investment in loans	10,597	11,926
Financing Receivable, Collectively Evaluated for Impairment	1,166,231	1,168,942
Premium wine
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	0	0
Financing Receivable, Individually Evaluated for Impairment	1,373	1,442
Recorded investment in loans	3,546	3,914
Financing Receivable, Collectively Evaluated for Impairment	720,340	663,392
Other
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	118	156
Financing Receivable, Individually Evaluated for Impairment	499	690
Recorded investment in loans	3,100	3,524
Financing Receivable, Collectively Evaluated for Impairment	$ 350,991	$ 395,954