Summary of Significant Accounting Policies - Additional Information (Details)			12 Months Ended
		Jan. 01, 2020 USD ($)	Dec. 31, 2020 USD ($) portfolio_segment class_financing_receivable	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Significant Accounting Policies [Line Items]
Number of portfolio segments | portfolio_segment			6
Number of classes of financing receivables | class_financing_receivable			11
Financing receivable, allowance for credit loss, forecast period			3 years
Finance lease obligations			$ 0	$ 0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			(8,433,491,000)	(6,621,080,000)	$ (5,264,843,000)	$ (4,319,415,000)
Allowance for Loan and Lease Losses, Period Increase (Decrease)		$ 48,500,000
Retained Earnings
Significant Accounting Policies [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			(5,671,749,000)	(4,575,601,000)	$ (3,791,838,000)	$ (2,866,837,000)
Cumulative adjustment for adoption of amendment | ASC 326
Significant Accounting Policies [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	[1]			35,049,000
Cumulative adjustment for adoption of amendment | ASC 326 | Retained Earnings
Significant Accounting Policies [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	[1]			35,049,000
Accrued Interest Receivable And Other Assets | Loans Receivable
Significant Accounting Policies [Line Items]
Interest receivable			126,400,000	119,100,000
Accrued Interest Receivable And Other Assets | Held-to-maturity securities
Significant Accounting Policies [Line Items]
Interest receivable			$ 55,000,000.0	$ 45,200,000
Investor dependent
Significant Accounting Policies [Line Items]
Number of loan portfolio segments | portfolio_segment			2
Investor dependent | Early stage
Significant Accounting Policies [Line Items]
Risk-based segments, revenue threshold of subcategories			$ 5,000,000
Investor dependent | Later stage
Significant Accounting Policies [Line Items]
Risk-based segments, revenue threshold of subcategories			$ 15,000,000
Lower Limit
Significant Accounting Policies [Line Items]
Term of contract on forward contracts			1 year
Sponsor equity contribution, percentage of acquisition price			50.00%
Lower Limit | Investor dependent | Mid stage
Significant Accounting Policies [Line Items]
Risk-based segments, revenue threshold of subcategories			$ 5,000,000
Upper Limit
Significant Accounting Policies [Line Items]
Ownership interest percentage			5.00%
Term of contract on forward contracts			5 years
Upper Limit | Mid stage
Significant Accounting Policies [Line Items]
Risk-based segments, revenue threshold of subcategories			$ 15,000,000
Equity warrant assets (public portfolio) | Lower Limit
Significant Accounting Policies [Line Items]
Duration of the sale restrictions			3 months
Equity warrant assets (public portfolio) | Upper Limit
Significant Accounting Policies [Line Items]
Duration of the sale restrictions			6 months
Equity warrant assets (public portfolio) | Sales restrictions discount | Lower Limit
Significant Accounting Policies [Line Items]
Sales restriction discounts			0.10
Equity warrant assets (public portfolio) | Sales restrictions discount | Upper Limit
Significant Accounting Policies [Line Items]
Sales restriction discounts			0.20
Non-marketable securities | Other investments | SPD Silicon Valley Bank Co., Ltd. | Equity method investee
Significant Accounting Policies [Line Items]
Ownership interest percentage			50.00%
Non-marketable securities | Lower Limit | Consolidated venture capital and private equity fund investments | Equity method investee
Significant Accounting Policies [Line Items]
Ownership interest percentage			20.00%
Non-marketable securities | Lower Limit | Investments in limited partnerships | Equity method investee
Significant Accounting Policies [Line Items]
Ownership interest percentage			5.00%
Non-marketable securities | Fair value accounting | Consolidated venture capital and private equity fund investments | Growth Partners, LP
Significant Accounting Policies [Line Items]
Ownership interest percentage			33.00%	33.00%
Non-marketable securities | Fair value accounting | Consolidated venture capital and private equity fund investments | Capital Preferred Return Fund, LP
Significant Accounting Policies [Line Items]
Ownership interest percentage			20.00%	20.00%
Non-marketable securities | Fair value accounting | Consolidated venture capital and private equity fund investments | Strategic Investors Fund, LP
Significant Accounting Policies [Line Items]
Ownership interest percentage			12.60%	12.60%
Non-marketable securities | Fair value accounting | Consolidated venture capital and private equity fund investments | CP I, LP
Significant Accounting Policies [Line Items]
Ownership interest percentage			0.00%	10.70%

[1] See Note 2- "Summary of Significant Accounting Policies" for additional details.