Loans and Allowance for Loan Losses - Composition of Loans, Net of Unearned Income (Detail) - Receivable Type [Domain] - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unearned income on loans	$ 110,000	$ 104,000
Loans, net of unearned income	14,261,430	14,384,276
Commercial Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	11,937,498	12,380,611
Commercial Portfolio Segment | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	4,980,553	4,954,676
Commercial Portfolio Segment | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,048,848	1,131,006
Commercial Portfolio Segment | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	3,987,448	4,582,906
Commercial Portfolio Segment | Life science & healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,475,568	1,289,904
Commercial Portfolio Segment | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	190,997	187,568
Commercial Portfolio Segment | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	254,084	234,551
Commercial Real Estate Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	2,006,005	1,764,519
Commercial Real Estate Portfolio Segment | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	632,410	606,753
Commercial Real Estate Portfolio Segment | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,340,316	1,118,115
Commercial Real Estate Portfolio Segment | Other real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	33,279	39,651
Construction Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	91,207	78,626
Consumer Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,567,036	1,278,635
Consumer Portfolio Segment | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,340,316	1,118,115
Consumer Portfolio Segment | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 226,720	$ 160,520