Loans and Allowance for Loan Losses - Composition of Loans, Net of Unearned Income (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 16,742,070	$ 14,384,276
Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	14,970,747	13,105,641
Commercial loans | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	5,437,915	4,954,676
Commercial loans | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,071,528	1,131,006
Commercial loans | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	5,467,577	4,582,906
Commercial loans | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,710,642	1,289,904
Commercial loans | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	847,295	794,321
Commercial loans | Commercial Other Financing Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	312,278	234,551
Commercial loans | Commercial Loans Receivable excluding Construction and Real Estate Secured
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	14,201,115	12,380,611
Commercial loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	435,790	352,828
Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	2,235,390	1,764,519
Real estate secured loans | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	646,120	606,753
Real estate secured loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	44,830	39,651
Construction Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	78,682	78,626
Consumer loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	226,883	160,520
Consumer loans | Real estate secured consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,544,440	1,118,115
Non-real Estate Secured Commercial Loans | Commercial loans | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 201,175	$ 187,568