Loans and Allowance for Loan Losses - Allowance for Loan Losses Individually and Collectively Evaluated for Impairment (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment, Allowance for loan losses	$ 50,865	$ 15,051
Individually Evaluated for Impairment, Recorded investment in loans	100,802	38,137
Collectively Evaluated for Impairment, Allowance for loan losses	141,779	150,308
Collectively Evaluated for Impairment, Allowance for loan losses	14,160,628	14,346,139
Commercial Portfolio Segment | Software and internet
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment, Allowance for loan losses	46,169	13,695
Individually Evaluated for Impairment, Recorded investment in loans	89,471	33,287
Collectively Evaluated for Impairment, Allowance for loan losses	60,559	67,286
Collectively Evaluated for Impairment, Allowance for loan losses	4,891,082	4,921,389
Commercial Portfolio Segment | Hardware
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment, Allowance for loan losses	481	1,133
Individually Evaluated for Impairment, Recorded investment in loans	2,357	2,521
Collectively Evaluated for Impairment, Allowance for loan losses	19,991	24,727
Collectively Evaluated for Impairment, Allowance for loan losses	1,046,491	1,128,485
Commercial Portfolio Segment | Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment, Allowance for loan losses	0	0
Individually Evaluated for Impairment, Recorded investment in loans	0	0
Collectively Evaluated for Impairment, Allowance for loan losses	29,276	27,997
Collectively Evaluated for Impairment, Allowance for loan losses	3,987,448	4,582,906
Commercial Portfolio Segment | Life science & healthcare
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment, Allowance for loan losses	1,616	121
Individually Evaluated for Impairment, Recorded investment in loans	2,433	475
Collectively Evaluated for Impairment, Allowance for loan losses	15,617	15,087
Collectively Evaluated for Impairment, Allowance for loan losses	1,473,135	1,289,429
Commercial Portfolio Segment | Premium wine
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment, Allowance for loan losses	0	0
Individually Evaluated for Impairment, Recorded investment in loans	1,236	1,304
Collectively Evaluated for Impairment, Allowance for loan losses	4,409	4,473
Collectively Evaluated for Impairment, Allowance for loan losses	822,171	793,017
Commercial Portfolio Segment | Other
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment, Allowance for loan losses	2,532	71
Individually Evaluated for Impairment, Recorded investment in loans	5,066	233
Collectively Evaluated for Impairment, Allowance for loan losses	3,362	3,182
Collectively Evaluated for Impairment, Allowance for loan losses	373,504	352,595
Commercial Portfolio Segment | Commercial loans
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment, Allowance for loan losses	50,798	15,020
Individually Evaluated for Impairment, Recorded investment in loans	100,563	37,820
Collectively Evaluated for Impairment, Allowance for loan losses	133,214	142,752
Collectively Evaluated for Impairment, Allowance for loan losses	12,593,831	13,067,821
Consumer Portfolio Segment | Consumer loans
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment, Allowance for loan losses	67	31
Individually Evaluated for Impairment, Recorded investment in loans	239	317
Collectively Evaluated for Impairment, Allowance for loan losses	8,565	7,556
Collectively Evaluated for Impairment, Allowance for loan losses	$ 1,566,797	$ 1,278,318