Loans, Allowance for Loan Losses and Allowance for Unfunded Credit Commitments - Composition of Loans, Net of Unearned Income, Broken Out by Portfolio Segment and Class of Financing Receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Unearned income on loans	$ 170,000	$ 173,000
Loans, net of unearned income	28,850,445	28,338,280
Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	25,751,037	25,304,637
Commercial loans | Software/internet
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	6,236,266	6,154,755
Commercial loans | Hardware
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	1,256,891	1,234,557
Commercial loans | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	14,308,077	14,110,560
Commercial loans | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	2,522,731	2,385,612
Commercial loans | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	1,014,975	959,663
Commercial loans | Other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	412,097	459,490
Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	3,099,408	3,033,643
Consumer loans | Other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	420,324	420,672
Consumer loans | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	$ 2,679,084	$ 2,612,971