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, 2015	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment, Allowance for loan losses	$ 23,822	$ 15,051
Individually Evaluated for Impairment, Recorded investment in loans	42,382	38,137
Collectively Evaluated for Impairment, Allowance for loan losses	144,053	150,308
Collectively Evaluated for Impairment, Allowance for loan losses	14,397,192	14,346,139
Software and internet
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment, Allowance for loan losses	20,942	13,695
Individually Evaluated for Impairment, Recorded investment in loans	34,716	33,287
Collectively Evaluated for Impairment, Allowance for loan losses	61,150	67,286
Collectively Evaluated for Impairment, Allowance for loan losses	4,836,858	4,921,389
Hardware
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment, Allowance for loan losses	12	1,133
Individually Evaluated for Impairment, Recorded investment in loans	510	2,521
Collectively Evaluated for Impairment, Allowance for loan losses	21,246	24,727
Collectively Evaluated for Impairment, Allowance for loan losses	1,066,876	1,128,485
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	30,837	27,997
Collectively Evaluated for Impairment, Allowance for loan losses	4,508,670	4,582,906
Life science & healthcare
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment, Allowance for loan losses	63	121
Individually Evaluated for Impairment, Recorded investment in loans	250	475
Collectively Evaluated for Impairment, Allowance for loan losses	15,260	15,087
Collectively Evaluated for Impairment, Allowance for loan losses	1,399,199	1,289,429
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	1,270	1,304
Collectively Evaluated for Impairment, Allowance for loan losses	4,503	4,473
Collectively Evaluated for Impairment, Allowance for loan losses	797,914	793,017
Other
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment, Allowance for loan losses	2,705	71
Individually Evaluated for Impairment, Recorded investment in loans	5,356	233
Collectively Evaluated for Impairment, Allowance for loan losses	3,446	3,182
Collectively Evaluated for Impairment, Allowance for loan losses	408,760	352,595
Commercial loans
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment, Allowance for loan losses	23,722	15,020
Individually Evaluated for Impairment, Recorded investment in loans	42,102	37,820
Collectively Evaluated for Impairment, Allowance for loan losses	136,442	142,752
Collectively Evaluated for Impairment, Allowance for loan losses	13,018,277	13,067,821
Consumer loans
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment, Allowance for loan losses	100	31
Individually Evaluated for Impairment, Recorded investment in loans	280	317
Collectively Evaluated for Impairment, Allowance for loan losses	7,611	7,556
Collectively Evaluated for Impairment, Allowance for loan losses	$ 1,378,915	$ 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=35738203&loc=SL6953423-111524

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- Definition

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

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (h)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524

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