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	Sep. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Unearned income on loans	$ 117,000	$ 115,000
Loans, net of unearned income	19,112,265	16,742,070
Commercial Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	16,245,107	14,201,115
Commercial Portfolio Segment | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	5,393,425	5,437,915
Commercial Portfolio Segment | Hardware
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	1,147,830	1,071,528
Commercial Portfolio Segment | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	7,412,238	5,467,577
Commercial Portfolio Segment | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	1,732,917	1,710,642
Commercial Portfolio Segment | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	872,031	847,295
Commercial Portfolio Segment | Other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	477,088	435,790
Commercial and Commercial Real Estate Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	17,035,529	14,970,747
Consumer Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	2,076,736	1,771,323
Consumer Portfolio Segment | Other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	241,106	226,883
Consumer Portfolio Segment | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	$ 1,835,630	$ 1,544,440