Loans and Allowance for Loan Losses - Allowance for Loan Losses Individually and Collectively Evaluated for Impairment (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	$ 2,325	$ 21,277
Financing Receivable, Individually Evaluated for Impairment	11,687	51,648
Recorded investment in loans	126,736	121,609
Financing Receivable, Collectively Evaluated for Impairment	12,005,494	10,854,738
Software
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	2,057	11,261
Financing Receivable, Individually Evaluated for Impairment	8,730	27,617
Recorded investment in loans	56,143	52,823
Financing Receivable, Collectively Evaluated for Impairment	4,494,639	4,075,019
Hardware
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	0	9,673
Financing Receivable, Individually Evaluated for Impairment	0	19,667
Recorded investment in loans	24,741	26,880
Financing Receivable, Collectively Evaluated for Impairment	1,072,102	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	19,849	16,366
Financing Receivable, Collectively Evaluated for Impairment	2,921,184	2,386,015
Life science
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	191	0
Financing Receivable, Individually Evaluated for Impairment	1,000	1,278
Recorded investment in loans	12,050	11,926
Financing Receivable, Collectively Evaluated for Impairment	1,244,527	1,168,942
Premium wine
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	0	0
Financing Receivable, Individually Evaluated for Impairment	1,339	1,442
Recorded investment in loans	4,221	3,914
Financing Receivable, Collectively Evaluated for Impairment	748,229	663,392
Other
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	4	156
Financing Receivable, Individually Evaluated for Impairment	186	690
Recorded investment in loans	2,918	3,524
Financing Receivable, Collectively Evaluated for Impairment	351,883	395,954
Commercial loans
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	2,252	21,109
Financing Receivable, Individually Evaluated for Impairment	11,255	50,733
Recorded investment in loans	119,922	115,433
Financing Receivable, Collectively Evaluated for Impairment	10,832,564	9,882,687
Consumer loans
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	73	168
Financing Receivable, Individually Evaluated for Impairment	432	915
Recorded investment in loans	6,814	6,176
Financing Receivable, Collectively Evaluated for Impairment	$ 1,172,930	$ 972,051