Loans, Allowance for Loan Losses and Allowance for Unfunded Credit Commitments - Composition of Loans, Net of Unearned Income (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unearned income on loans	$ 170,000	$ 173,000
Loans, net of unearned income	28,850,445	28,338,280
Commercial loans, excluding real estate secured and construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	24,840,192	24,456,728
Commercial loans, excluding real estate secured and construction | Software/internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	6,236,266	6,154,755
Commercial loans, excluding real estate secured and construction | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,256,891	1,234,557
Commercial loans, excluding real estate secured and construction | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	14,308,077	14,110,560
Commercial loans, excluding real estate secured and construction | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	2,522,731	2,385,612
Commercial loans, excluding real estate secured and construction | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	256,021	249,266
Commercial loans, excluding real estate secured and construction | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	260,206	321,978
Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	3,478,075	3,363,803
Real estate secured loans | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	758,954	710,397
Real estate secured loans | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	2,679,084	2,612,971
Real estate secured loans | Other real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	40,037	40,435
Construction loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	111,854	97,077
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	3,099,408	3,033,643
Consumer loans | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	2,679,084	2,612,971
Consumer loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 420,324	$ 420,672