Loans and Allowance for Loan Losses - Composition of Loans, Net of Unearned income (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 9,622,172	[1]	$ 8,946,933	[1]
Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,244,444		1,098,813
Commercial Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	8,756,728		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	8,224,179		7,637,721
Commercial Portfolio Segment | Software
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	3,558,323		3,261,489
Commercial Portfolio Segment | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,205,541		1,118,370
Commercial Portfolio Segment | Venture capital/private equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,923,516		1,732,699
Commercial Portfolio Segment | Life science
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,084,720		1,066,199
Commercial Portfolio Segment | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	608,524		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	142,562		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	465,962	[2]	413,513	[2]
Commercial Portfolio Segment | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	376,104		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	309,517		315,453
Commercial Portfolio Segment | Other | Construction loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	66,587		65,742
Consumer Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	865,444		829,957
Consumer Portfolio Segment | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	778,482	[3]	685,300	[3]
Consumer Portfolio Segment | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 86,962		$ 144,657

[1] Included within our total loan portfolio are credit card loans of $78 million and $64 million at June 30, 2013 and December 31, 2012, respectively.

[2] Included in our premium wine portfolio are gross construction loans of $132 million and $148 million at June 30, 2013 and December 31, 2012, respectively.

[3] Consumer loans secured by real estate at June 30, 2013 and December 31, 2012 were comprised of the following:(Dollars in thousands) June 30, 2013 December 31, 2012Loans for personal residence $593,988 $503,378Loans to eligible employees 115,974 110,584Home equity lines of credit 68,520 71,338Consumer loans secured by real estate $778,482 $685,300