Loans and Allowance for Loan Losses - Average Impaired Loans, Broken out by Portfolio Segment and Class of Financing Receivable (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 193,120	$ 176,412	$ 95,188
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	3,566	3,884	1,070
Commercial loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	189,802	174,688	94,975
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	3,566	3,867	1,070
Commercial loans \| Software and internet
Financing Receivable, Impaired [Line Items]
Average impaired loans	119,557	89,462	63,825
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	2,263	1,054	344
Commercial loans \| Hardware
Financing Receivable, Impaired [Line Items]
Average impaired loans	35,022	39,108	8,854
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	1,061	2,624	574
Commercial loans \| Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Average impaired loans	556	0	0
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	0	0	0
Commercial loans \| Life science/healthcare
Financing Receivable, Impaired [Line Items]
Average impaired loans	30,842	40,620	18,083
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	90	155	132
Commercial loans \| Premium wine
Financing Receivable, Impaired [Line Items]
Average impaired loans	3,249	2,056	1,455
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	152	28	12
Commercial loans \| Other
Financing Receivable, Impaired [Line Items]
Average impaired loans	576	3,442	2,758
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	0	6	8
Consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	3,318	1,724	213
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	0	17	0
Consumer loans \| Real estate secured consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	1,514	588	172
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	0	0	0
Consumer loans \| Other Loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	1,804	1,136	41
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	$ 0	$ 17	$ 0

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- Definition

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5258-111524

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Amount of interest income, recognized on accrual basis, on financing receivables, for which there is a related allowance for credit losses and are recognized as impaired.

+ References

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