Loans and Allowance for Loan Losses - Recorded Investment in Loans Modified in TDRs (Detail) $ in Thousands	12 Months Ended
Dec. 31, 2017 USD ($) troubled_debt_restructuring	Dec. 31, 2016 USD ($) troubled_debt_restructuring	Dec. 31, 2015 USD ($)
Financing Receivable, Modifications [Line Items]
Number of TDRs \| troubled_debt_restructuring	22	20
Loans modified in TDRs during the period	$ 93,843	$ 41,545	$ 110,371
Partial charge-offs on loans classified as TDRs	3,000	3,600	23,500
Commercial loans
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	93,843	40,759	110,371
Commercial loans \| Software and internet
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	42,184	23,574	56,790
Commercial loans \| Hardware
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	51,132	14,870	286
Commercial loans \| Private equity/venture capital
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	350	0	0
Commercial loans \| Life science/healthcare
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	0	1,638	51,878
Commercial loans \| Premium wine
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	177	677	898
Commercial loans \| Other
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	0	0	519
Consumer loans \| Other
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	0	$ 786	$ 0
Payment Deferrals Granted
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	93,500
Forgiveness Of Principal
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	$ 300

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings during the period.

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953682-111524

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- Definition

Reflects the amount of the write-down related to a troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=82895541&loc=d3e18845-111554

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