Loans and Allowance for Loan Losses - Composition of Loans, Net of Unearned income (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 14,439,574	[1]	$ 14,384,276	[1]
Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,861,689		1,764,519
Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	4,871,574		4,954,676
Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,067,386		1,131,006
Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	4,508,670		4,582,906
Life science & healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,399,449		1,289,904
Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	799,184		794,321
Premium wine | Non-real Estate Secured Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	186,070		187,568
Premium wine | Real Estate Secured Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	613,114	[2]	606,753	[2]
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	414,116		352,828
Other | Commercial Loans Receivable excluding Construction and Real Estate Secured
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	289,010		234,551
Other | Construction loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	85,684		78,626
Commercial Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	13,060,379		13,105,641
Commercial Portfolio Segment | Commercial Loans Receivable excluding Construction and Real Estate Secured
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	12,322,159		12,380,611
Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,209,153		1,118,115
Real estate secured loans | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,209,153	[3]	1,118,115	[3]
Other | Real Estate Secured Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	39,422		39,651
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 170,042		$ 160,520

[1] Included within our total loan portfolio are credit card loans of $154 million and $131 million at March 31, 2015 and December 31, 2014, respectively.

[2] Included in our premium wine portfolio are gross construction loans of $108 million and $112 million at March 31, 2015 and December 31, 2014, respectively.

[3] Consumer loans secured by real estate at March 31, 2015 and December 31, 2014 were comprised of the following:(Dollars in thousands) March 31, 2015 December 31, 2014Loans for personal residence $1,001,125 $918,629Loans to eligible employees 139,761 133,568Home equity lines of credit 68,267 65,918Consumer loans secured by real estate $1,209,153 $1,118,115