Loans and Allowance for Loan Losses - Allowance for Loan Losses Individually and Collectively Evaluated for Impairment (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	$ 6,776	$ 21,277
Financing Receivable, Individually Evaluated for Impairment	24,989	51,648
Recorded investment in loans	116,766	121,609
Financing Receivable, Collectively Evaluated for Impairment	10,808,919	10,854,738
Commercial loans
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	6,664	21,109
Financing Receivable, Individually Evaluated for Impairment	24,303	50,733
Recorded investment in loans	110,741	115,433
Financing Receivable, Collectively Evaluated for Impairment	9,791,141	9,882,687
Consumer loans
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	112	168
Financing Receivable, Individually Evaluated for Impairment	686	915
Recorded investment in loans	6,025	6,176
Financing Receivable, Collectively Evaluated for Impairment	1,017,778	972,051
Software
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	4,652	11,261
Financing Receivable, Individually Evaluated for Impairment	11,761	27,617
Recorded investment in loans	50,589	52,823
Financing Receivable, Collectively Evaluated for Impairment	4,114,062	4,075,019
Hardware
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	979	9,673
Financing Receivable, Individually Evaluated for Impairment	7,886	19,667
Recorded investment in loans	24,257	26,880
Financing Receivable, Collectively Evaluated for Impairment	1,185,297	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	17,676	16,366
Financing Receivable, Collectively Evaluated for Impairment	2,201,243	2,386,015
Life science
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	231	0
Financing Receivable, Individually Evaluated for Impairment	909	1,278
Recorded investment in loans	11,243	11,926
Financing Receivable, Collectively Evaluated for Impairment	1,170,349	1,168,942
Premium wine
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	0	0
Financing Receivable, Individually Evaluated for Impairment	1,408	1,442
Recorded investment in loans	3,737	3,914
Financing Receivable, Collectively Evaluated for Impairment	699,971	663,392
Other
Financing Receivable, Impaired [Line Items]
Recorded investment in loans	802	156
Financing Receivable, Individually Evaluated for Impairment	2,339	690
Recorded investment in loans	3,239	3,524
Financing Receivable, Collectively Evaluated for Impairment	$ 420,219	$ 395,954