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, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	$ 105,711	$ 94,326	$ 102,669	$ 104,045	$ 96,641	$ 94,142
Nonaccrual Loans with no Allowance for Credit Loss	6,737		7,230
Global fund banking
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	13	9	0	0	0	3,700
Nonaccrual Loans with no Allowance for Credit Loss	8		0
Investor dependent
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	69,934	43,039	34,719	51,452	77,335	23,752
Nonaccrual Loans with no Allowance for Credit Loss	10		734
Cash flow dependent
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	27,877	26,975	62,266	45,111	8,444	56,690
Nonaccrual Loans with no Allowance for Credit Loss	705		2,782
SVB Private Bank
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	5,432	6,517	5,480	7,089	5,644	3,919
Nonaccrual Loans with no Allowance for Credit Loss	4,912		3,714
Balance sheet dependent
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	676	11,842	0	0	4,974	5,004
Nonaccrual Loans with no Allowance for Credit Loss	0		0
Premium wine
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	1,675	1,681	204	393	244	285
Nonaccrual Loans with no Allowance for Credit Loss	998		0
Other
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	104	61	0	0	0	792
Nonaccrual Loans with no Allowance for Credit Loss	104		0
SBA loans
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	0	4,202	0
Nonaccrual Loans with no Allowance for Credit Loss	0		0
Early stage | Investor dependent
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	19,732	24,422	11,093	18,958	10,290	7,616
Nonaccrual Loans with no Allowance for Credit Loss	10		460
Mid stage | Investor dependent
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	11,627	8,119	17,330	5,231	28,699	4,751
Nonaccrual Loans with no Allowance for Credit Loss	0		274
Later stage | Investor dependent
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	38,575	10,498	6,296	27,263	38,346	11,385
Nonaccrual Loans with no Allowance for Credit Loss	0		0
Sponsor led buyout | Cash flow dependent
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	21,592	21,658	44,585	45,019	8,365	39,534
Nonaccrual Loans with no Allowance for Credit Loss	0		0
Other | Cash flow dependent
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans	6,285	$ 5,317	17,681	$ 92	$ 79	$ 17,156
Nonaccrual Loans with no Allowance for Credit Loss	$ 705		$ 2,782