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	Jun. 30, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	$ 11,348,711	$ 10,906,386
Commercial Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	10,242,165	9,933,420
Consumer Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	1,106,546	972,966
Software
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	4,212,190	4,102,636
Hardware
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	1,144,144	1,213,032
Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	2,646,397	2,386,054
Life science
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	1,166,231	1,170,220
Premium wine
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	721,713	664,834
Other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	351,490	396,644
Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	984,583	873,255
Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	$ 121,963	$ 99,711