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	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Unearned income on loans	$ 165,000	$ 173,000
Loans, net of unearned income	31,063,994	28,338,280
Commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	27,567,526	25,304,637
Commercial loans | Software/internet
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	6,009,518	6,154,755
Commercial loans | Hardware
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	1,357,617	1,234,557
Commercial loans | Private equity/venture capital
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	16,293,556	14,110,560
Commercial loans | Life science/healthcare
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	2,381,822	2,385,612
Commercial loans | Premium wine
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	983,814	959,663
Commercial loans | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	541,199	459,490
Consumer loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	3,496,468	3,033,643
Consumer loans | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	481,072	420,672
Consumer loans | Real estate secured loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 3,015,396	$ 2,612,971