Loans, Allowance for Loan Losses and Allowance for Unfunded Credit Commitments - Composition of Loans, Net of Unearned Income (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unearned income on loans	$ 141,000	$ 125,000
Loans, net of unearned income	22,189,327	19,899,944
Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Construction	104,000	110,000
Commercial Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	18,852,453	16,945,288
Commercial Portfolio Segment \| Software/internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	5,793,637	5,627,031
Commercial Portfolio Segment \| Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,113,509	1,180,398
Commercial Portfolio Segment \| Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	9,623,824	7,691,148
Commercial Portfolio Segment \| Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,725,728	1,853,004
Commercial Portfolio Segment \| Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	924,116	878,322
Commercial Portfolio Segment \| Premium wine \| Non-real estate secured commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	211,716	200,156
Commercial Portfolio Segment \| Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	384,039	393,551
Commercial Portfolio Segment \| Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	501,785	501,709
Commercial Real Estate Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	2,961,405	2,648,621
Commercial Real Estate Portfolio Segment \| Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	712,400	678,166
Commercial Real Estate Portfolio Segment \| Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	2,206,501	1,926,968
Commercial Real Estate Portfolio Segment \| Other real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	42,504	43,487
Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	75,242	64,671
Consumer Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	2,506,728	2,168,332
Consumer Portfolio Segment \| Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	2,206,501	1,926,968
Consumer Portfolio Segment \| Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 300,227	$ 241,364

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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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