Loans and Allowance for Loan Losses - Composition of Loans, Net of Unearned Income (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unearned income on loans	$ 117,000	$ 115,000
Loans, net of unearned income	19,112,265	16,742,070
Commercial Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	16,245,107	14,201,115
Commercial Portfolio Segment | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	5,393,425	5,437,915
Commercial Portfolio Segment | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,147,830	1,071,528
Commercial Portfolio Segment | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	7,412,238	5,467,577
Commercial Portfolio Segment | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,732,917	1,710,642
Commercial Portfolio Segment | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	872,031	847,295
Commercial Portfolio Segment | Premium wine | Non-real estate secured commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	190,223	201,175
Commercial Portfolio Segment | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	368,474	312,278
Commercial Portfolio Segment | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	477,088	435,790
Commercial Real Estate Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	2,561,363	2,235,390
Commercial Real Estate Portfolio Segment | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	681,808	646,120
Commercial Real Estate Portfolio Segment | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,835,630	1,544,440
Commercial Real Estate Portfolio Segment | Other real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	43,925	44,830
Construction Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	64,689	78,682
Consumer Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	2,076,736	1,771,323
Consumer Portfolio Segment | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,835,630	1,544,440
Consumer Portfolio Segment | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 241,106	$ 226,883