Loans and Allowance for Loan Losses - Composition of Loans, Net of Unearned Income (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 19,899,944	$ 16,742,070
Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	17,731,612	14,970,747
Commercial loans | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	5,627,031	5,437,915
Commercial loans | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,180,398	1,071,528
Commercial loans | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	7,691,148	5,467,577
Commercial loans | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,853,004	1,710,642
Commercial loans | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	878,322	847,295
Commercial loans | Commercial Other Financing Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	393,551	312,278
Commercial loans | Commercial Loans Receivable excluding Construction and Real Estate Secured
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	16,945,288	14,201,115
Commercial loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	501,709	435,790
Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	2,648,621	2,235,390
Real estate secured loans | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	678,166	646,120
Real estate secured loans | Real estate secured consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,926,968	1,544,440
Real estate secured loans | Other Real Estate Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	43,487	44,830
Construction Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	64,671	78,682
Consumer loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	241,364	226,883
Consumer loans | Real estate secured consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,926,968	1,544,440
Non-real Estate Secured Commercial Loans | Commercial loans | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	200,156	201,175
Loans for personal residence | Consumer loans | Real estate secured consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,655,349	1,312,818
Loans to eligible employees | Consumer loans | Real estate secured consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	199,291	156,001
Home equity lines of credit | Consumer loans | Real estate secured consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 72,328	$ 75,621