Loans and Allowance for Loan Losses - Allowance for Loan Losses Individually and Collectively Evaluated for Impairment (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment, Allowance for loan losses	$ 46,256	$ 15,051
Individually Evaluated for Impairment, Recorded investment in loans	115,461	38,137
Collectively Evaluated for Impairment, Allowance for loan losses	151,251	150,308
Collectively Evaluated for Impairment, Allowance for loan losses	15,199,119	14,346,139
Commercial Portfolio Segment \| Software and internet
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment, Allowance for loan losses	25,260	13,695
Individually Evaluated for Impairment, Recorded investment in loans	64,792	33,287
Collectively Evaluated for Impairment, Allowance for loan losses	62,806	67,286
Collectively Evaluated for Impairment, Allowance for loan losses	5,208,033	4,921,389
Commercial Portfolio Segment \| Hardware
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment, Allowance for loan losses	1,100	1,133
Individually Evaluated for Impairment, Recorded investment in loans	3,763	2,521
Collectively Evaluated for Impairment, Allowance for loan losses	19,542	24,727
Collectively Evaluated for Impairment, Allowance for loan losses	958,532	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	32,442	27,997
Collectively Evaluated for Impairment, Allowance for loan losses	4,571,102	4,582,906
Commercial Portfolio Segment \| Life science & healthcare
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment, Allowance for loan losses	19,739	121
Individually Evaluated for Impairment, Recorded investment in loans	45,389	475
Collectively Evaluated for Impairment, Allowance for loan losses	17,220	15,087
Collectively Evaluated for Impairment, Allowance for loan losses	1,552,973	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	1,201	1,304
Collectively Evaluated for Impairment, Allowance for loan losses	4,662	4,473
Collectively Evaluated for Impairment, Allowance for loan losses	825,759	793,017
Commercial Portfolio Segment \| Other
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment, Allowance for loan losses	157	71
Individually Evaluated for Impairment, Recorded investment in loans	157	233
Collectively Evaluated for Impairment, Allowance for loan losses	4,616	3,182
Collectively Evaluated for Impairment, Allowance for loan losses	425,987	352,595
Commercial Portfolio Segment \| Commercial loans
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment, Allowance for loan losses	46,256	15,020
Individually Evaluated for Impairment, Recorded investment in loans	115,302	37,820
Collectively Evaluated for Impairment, Allowance for loan losses	141,288	142,752
Collectively Evaluated for Impairment, Allowance for loan losses	13,542,386	13,067,821
Consumer Portfolio Segment \| Consumer loans
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment, Allowance for loan losses	0	31
Individually Evaluated for Impairment, Recorded investment in loans	159	317
Collectively Evaluated for Impairment, Allowance for loan losses	9,963	7,556
Collectively Evaluated for Impairment, Allowance for loan losses	$ 1,656,733	$ 1,278,318

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (h)

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The balance of financing receivables that were individually evaluated for impairment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (h)

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