Loans, Allowance for Loan Losses and Allowance for Unfunded Credit Commitments - Nonaccrual Loans with No Allowance for Credit Loss (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	$ 114,000	$ 104,000
Nonaccrual Loans with no Allowance for Credit Loss	19,000	8,000
Boston Private
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	31,000
Investor dependent
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	30,000	51,000
Nonaccrual Loans with no Allowance for Credit Loss	0	3,000
Investor dependent | Early stage
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	4,000	18,000
Nonaccrual Loans with no Allowance for Credit Loss	0	0
Investor dependent | Growth stage
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	26,000	33,000
Nonaccrual Loans with no Allowance for Credit Loss	0	3,000
Cash flow dependent and innovation C&I (Commercial and Industrial) | Cash flow dependent - SLBO
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	34,000	40,000
Nonaccrual Loans with no Allowance for Credit Loss	0	0
Cash flow dependent and innovation C&I (Commercial and Industrial) | Innovation C&I
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	0	6,000
Nonaccrual Loans with no Allowance for Credit Loss	0	1,000
Private bank
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	11,000	6,000
Nonaccrual Loans with no Allowance for Credit Loss	2,000	3,000
CRE
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	19,000	0
Nonaccrual Loans with no Allowance for Credit Loss	0	0
Premium wine and other | Premium wine
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	17,000	1,000
Nonaccrual Loans with no Allowance for Credit Loss	17,000	1,000
Other C&I
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	3,000	0
Nonaccrual Loans with no Allowance for Credit Loss	$ 0	$ 0