Loans and Allowance for Loan Losses - Composition of Loans, Net of Unearned income (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 8,844,890	[1]	$ 8,946,933	[1]
Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,189,607		1,098,813
Commercial Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	8,020,707		8,116,976
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	7,497,421		7,637,721
Commercial Portfolio Segment | Software
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	3,455,602		3,261,489
Commercial Portfolio Segment | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,220,691		1,118,370
Commercial Portfolio Segment | Venture capital/private equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,322,123		1,732,699
Commercial Portfolio Segment | Life science
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,017,859		1,066,199
Commercial Portfolio Segment | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	603,730		557,024
Commercial Portfolio Segment | Premium wine | Non-real Estate Secured Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	139,017		143,511
Commercial Portfolio Segment | Premium wine | Real Estate Secured Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	464,713	[2]	413,513	[2]
Commercial Portfolio Segment | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	400,702		381,195
Commercial Portfolio Segment | Other | Commercial Loans Receivable excluding Construction and Real Estate Secured
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	342,129		315,453
Commercial Portfolio Segment | Other | Construction loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	58,573		65,742
Consumer Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	824,183		829,957
Consumer Portfolio Segment | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	724,894	[3]	685,300	[3]
Consumer Portfolio Segment | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 99,289		$ 144,657

[1] Included within our total loan portfolio are credit card loans of $77 million and $64 million at March 31, 2013 and December 31, 2012, respectively.

[2] Included in our premium wine portfolio are gross construction loans of $133 million and $148 million at March 31, 2013 and December 31, 2012, respectively.

[3] Consumer loans secured by real estate at March 31, 2013 and December 31, 2012 were comprised of the following:(Dollars in thousands) March 31, 2013 December 31, 2012Loans for personal residence $541,115 $503,378Loans to eligible employees 112,314 110,584Home equity lines of credit 71,465 71,338Consumer loans secured by real estate $724,894 $685,300