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, 2017	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
Individually evaluated for impairment, allowance for loan losses	$ 48,370	$ 48,825
Individually evaluated for impairment, recorded investment in loans	198,293	234,460
Collectively evaluated for impairment, allowance for loan losses	188,126	176,541
Collectively evaluated for impairment, allowance for loan losses	20,778,173	19,665,484
Commercial Portfolio Segment \| Software/internet
Financing Receivable, Impaired [Line Items]
Individually evaluated for impairment, allowance for loan losses	30,291	28,245
Individually evaluated for impairment, recorded investment in loans	129,627	122,748
Collectively evaluated for impairment, allowance for loan losses	62,646	69,143
Collectively evaluated for impairment, allowance for loan losses	5,262,395	5,504,283
Commercial Portfolio Segment \| Hardware
Financing Receivable, Impaired [Line Items]
Individually evaluated for impairment, allowance for loan losses	5,329	9,995
Individually evaluated for impairment, recorded investment in loans	30,020	65,395
Collectively evaluated for impairment, allowance for loan losses	22,471	21,171
Collectively evaluated for impairment, allowance for loan losses	1,088,246	1,115,003
Commercial Portfolio Segment \| Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Individually evaluated for impairment, allowance for loan losses	31	0
Individually evaluated for impairment, recorded investment in loans	308	0
Collectively evaluated for impairment, allowance for loan losses	66,754	50,299
Collectively evaluated for impairment, allowance for loan losses	8,891,354	7,691,148
Commercial Portfolio Segment \| Life science/healthcare
Financing Receivable, Impaired [Line Items]
Individually evaluated for impairment, allowance for loan losses	11,223	8,709
Individually evaluated for impairment, recorded investment in loans	31,471	38,361
Collectively evaluated for impairment, allowance for loan losses	16,507	16,737
Collectively evaluated for impairment, allowance for loan losses	1,667,146	1,814,643
Commercial Portfolio Segment \| Premium wine
Financing Receivable, Impaired [Line Items]
Individually evaluated for impairment, allowance for loan losses	290	520
Individually evaluated for impairment, recorded investment in loans	3,167	3,187
Collectively evaluated for impairment, allowance for loan losses	2,843	3,595
Collectively evaluated for impairment, allowance for loan losses	901,802	875,135
Commercial Portfolio Segment \| Other
Financing Receivable, Impaired [Line Items]
Individually evaluated for impairment, allowance for loan losses	270	233
Individually evaluated for impairment, recorded investment in loans	408	867
Collectively evaluated for impairment, allowance for loan losses	3,865	4,535
Collectively evaluated for impairment, allowance for loan losses	566,362	500,842
Commercial Portfolio Segment \| Commercial loans
Financing Receivable, Impaired [Line Items]
Individually evaluated for impairment, allowance for loan losses	47,434	47,702
Individually evaluated for impairment, recorded investment in loans	195,001	230,558
Collectively evaluated for impairment, allowance for loan losses	175,086	165,480
Collectively evaluated for impairment, allowance for loan losses	18,377,305	17,501,054
Consumer Portfolio Segment \| Consumer loans
Financing Receivable, Impaired [Line Items]
Individually evaluated for impairment, allowance for loan losses	936	1,123
Individually evaluated for impairment, recorded investment in loans	3,292	3,902
Collectively evaluated for impairment, allowance for loan losses	13,040	11,061
Collectively evaluated for impairment, allowance for loan losses	$ 2,400,868	$ 2,164,430

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.

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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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