Loans, Allowance for Loan Losses and Allowance for Unfunded Credit Commitments - Composition of Loans, Net of Unearned Income, Broken Out by Portfolio Segment and Class of Financing Receivable (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Unearned income on loans	$ 121,000	$ 125,000
Loans, net of unearned income	20,427,451	19,899,944
Commercial Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	17,396,510	16,945,288
Commercial Portfolio Segment | Software/internet
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	5,458,203	5,627,031
Commercial Portfolio Segment | Hardware
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	1,097,835	1,180,398
Commercial Portfolio Segment | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	8,426,831	7,691,148
Commercial Portfolio Segment | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	1,735,987	1,853,004
Commercial Portfolio Segment | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	876,567	878,322
Commercial Portfolio Segment | Other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	587,954	501,709
Commercial and Commercial Real Estate Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	18,183,377	17,731,612
Consumer Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	2,244,074	2,168,332
Consumer Portfolio Segment | Other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	231,097	241,364
Consumer Portfolio Segment | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	$ 2,012,977	$ 1,926,968