Loans and Allowance for Loan Losses - Composition of Loans, Net of Unearned Income, Broken Out by Portfolio Segment and Class of Financing Receivable (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	$ 19,899,944	$ 16,742,070
Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	2,168,332	1,771,323
Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	17,731,612	14,970,747
Commercial loans | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	5,627,031	5,437,915
Commercial loans | Hardware
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	1,180,398	1,071,528
Commercial loans | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	7,691,148	5,467,577
Commercial loans | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	1,853,004	1,710,642
Commercial loans | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	878,322	847,295
Commercial loans | Other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	501,709	435,790
Consumer loans | Other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	241,364	226,883
Consumer loans | Real estate secured consumer loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	$ 1,926,968	$ 1,544,440