Loans, Allowance for Loan Losses and Allowance for Unfunded Credit Commitments - Composition of Loans, Net of Unearned Income (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unearned income on loans	$ 158,000	$ 148,000
Loans, net of unearned income	24,587,944	23,106,316
Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Construction	101,000	100,000
Commercial Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	21,097,918	19,697,163
Commercial Portfolio Segment \| Software/internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	6,209,084	6,172,531
Commercial Portfolio Segment \| Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,336,000	1,193,599
Commercial Portfolio Segment \| Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	11,211,816	9,952,377
Commercial Portfolio Segment \| Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,932,608	1,808,827
Commercial Portfolio Segment \| Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	865,024	873,158
Commercial Portfolio Segment \| Premium wine \| Non-real estate secured commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	188,943	204,105
Commercial Portfolio Segment \| Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	219,467	365,724
Commercial Portfolio Segment \| Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	320,125	476,338
Commercial Real Estate Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	3,080,067	3,011,627
Commercial Real Estate Portfolio Segment \| Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	676,081	669,053
Commercial Real Estate Portfolio Segment \| Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	2,362,340	2,300,506
Commercial Real Estate Portfolio Segment \| Other real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	41,646	42,068
Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	59,012	68,546
Consumer Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	2,713,287	2,629,486
Consumer Portfolio Segment \| Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	2,362,340	2,300,506
Consumer Portfolio Segment \| Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 350,947	$ 328,980

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Amount of deferred interest and fee income, unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of acquired loans. Excludes amounts for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 20
-Section 50
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-Publisher FASB
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-Section S99
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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
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Amount before allowance of commercial construction loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Topic 310
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5066-111524

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