Loans, Allowance for Loan Losses and Allowance for Unfunded Credit Commitments - Composition of Loans, Net of Unearned Income (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 28,338,280	$ 23,106,316
Commercial Loans Receivable excluding Construction and Real Estate Secured
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	24,456,728	19,697,163
Commercial Loans Receivable excluding Construction and Real Estate Secured | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	6,154,755	6,172,531
Commercial Loans Receivable excluding Construction and Real Estate Secured | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,234,557	1,193,599
Commercial Loans Receivable excluding Construction and Real Estate Secured | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	14,110,560	9,952,377
Commercial Loans Receivable excluding Construction and Real Estate Secured | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	2,385,612	1,808,827
Commercial Loans Receivable excluding Construction and Real Estate Secured | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	249,266	204,105
Commercial Loans Receivable excluding Construction and Real Estate Secured | Commercial Other Financing Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	321,978	365,724
Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	3,363,803	3,011,627
Real estate secured loans | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	710,397	669,053
Real estate secured loans | Real estate secured consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	2,612,971	2,300,506
Real estate secured loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	40,435	42,068
Construction Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	97,077	68,546
Consumer loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	420,672	328,980
Consumer loans | Real estate secured consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	2,612,971	2,300,506
Consumer loans | Real estate secured consumer loans | Loans for personal residence
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	2,251,292	1,995,840
Consumer loans | Real estate secured consumer loans | Loans to eligible employees
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	290,194	243,118
Consumer loans | Real estate secured consumer loans | Home equity lines of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 71,485	$ 61,548