Loans, Allowance for Loan Losses and Allowance for Unfunded Credit Commitments - Allowance for Loan Losses Individually and Collectively Evaluated for Impairment (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Impaired [Line Items]
Individually evaluated for impairment, allowance for loan losses	$ 53,677	$ 41,793
Individually evaluated for impairment, recorded investment in loans	178,179	174,861
Collectively evaluated for impairment, allowance for loan losses	233,032	213,231
Collectively evaluated for impairment, allowance for loan losses	25,818,013	22,931,455
Commercial loans \| Software/internet
Financing Receivable, Impaired [Line Items]
Individually evaluated for impairment, allowance for loan losses	25,320	23,088
Individually evaluated for impairment, recorded investment in loans	102,520	110,654
Collectively evaluated for impairment, allowance for loan losses	77,328	73,016
Collectively evaluated for impairment, allowance for loan losses	6,127,838	6,061,877
Commercial loans \| Hardware
Financing Receivable, Impaired [Line Items]
Individually evaluated for impairment, allowance for loan losses	13,392	8,450
Individually evaluated for impairment, recorded investment in loans	42,294	36,350
Collectively evaluated for impairment, allowance for loan losses	21,303	19,164
Collectively evaluated for impairment, allowance for loan losses	1,226,947	1,157,249
Commercial loans \| Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Individually evaluated for impairment, allowance for loan losses	0	330
Individually evaluated for impairment, recorded investment in loans	0	658
Collectively evaluated for impairment, allowance for loan losses	89,409	82,138
Collectively evaluated for impairment, allowance for loan losses	12,224,155	9,951,719
Commercial loans \| Life science/healthcare
Financing Receivable, Impaired [Line Items]
Individually evaluated for impairment, allowance for loan losses	14,442	9,315
Individually evaluated for impairment, recorded investment in loans	26,420	21,687
Collectively evaluated for impairment, allowance for loan losses	20,622	15,609
Collectively evaluated for impairment, allowance for loan losses	2,061,452	1,787,140
Commercial loans \| 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	2,524	2,877
Collectively evaluated for impairment, allowance for loan losses	3,438	3,532
Collectively evaluated for impairment, allowance for loan losses	881,646	870,281
Commercial loans \| Other
Financing Receivable, Impaired [Line Items]
Individually evaluated for impairment, allowance for loan losses	8	32
Individually evaluated for impairment, recorded investment in loans	8	32
Collectively evaluated for impairment, allowance for loan losses	2,888	3,909
Collectively evaluated for impairment, allowance for loan losses	422,047	476,306
Commercial loans \| Commercial loans
Financing Receivable, Impaired [Line Items]
Individually evaluated for impairment, allowance for loan losses	53,162	41,215
Individually evaluated for impairment, recorded investment in loans	173,766	172,258
Collectively evaluated for impairment, allowance for loan losses	214,988	197,368
Collectively evaluated for impairment, allowance for loan losses	22,944,085	20,304,572
Consumer loans \| Consumer loans
Financing Receivable, Impaired [Line Items]
Individually evaluated for impairment, allowance for loan losses	515	578
Individually evaluated for impairment, recorded investment in loans	4,413	2,603
Collectively evaluated for impairment, allowance for loan losses	18,044	15,863
Collectively evaluated for impairment, allowance for loan losses	$ 2,873,928	$ 2,626,883

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=84173941&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.

+ References

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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)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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+ 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)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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