Loans and Allowance for Loan Losses - Recorded Investment in Loans Modified in TDRs (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	$ 41,545	$ 110,371	$ 2,738
Partial charge-offs on loans classified as TDRs	3,600	23,500
Commercial loans
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	40,759	110,371	2,738
Commercial loans | Software and internet
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	23,574	56,790	1,033
Commercial loans | Hardware
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	14,870	286	1,118
Commercial loans | Private equity/venture capital
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	0	0	0
Commercial loans | Life science/healthcare
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	1,638	51,878	0
Commercial loans | Premium wine
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	677	898	587
Commercial loans | Other
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	0	519	0
Consumer loans
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	786	0	0
Consumer loans | Other
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period	$ 786	$ 0	0
Payment Deferrals Granted
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period			1,700
Forgiveness Of Principal
Financing Receivable, Modifications [Line Items]
Loans modified in TDRs during the period			$ 1,000