Loans and Allowance for Loan Losses - Composition of Loans, Net of Unearned Income, Broken Out by Portfolio Segment and Class of Financing Receivable (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	$ 14,439,574	[1]	$ 14,384,276	[1]
Software and internet
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	4,871,574		4,954,676
Hardware
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	1,067,386		1,131,006
Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	4,508,670		4,582,906
Life science & healthcare
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	1,399,449		1,289,904
Premium wine
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	799,184		794,321
Other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	414,116		352,828
Commercial Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	13,060,379		13,105,641
Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	1,209,153		1,118,115
Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	170,042		160,520
Consumer Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	$ 1,379,195		$ 1,278,635

[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.