Fair Value of Financial Instruments - Quantitative Information About Significant Unobservable Inputs (Additional Information) (Details)	3 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Equity warrant assets, private portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted average remaining life	2 years 9 months 18 days
Weighted average remaining life	6 years 2 months 12 days
Sales restrictions discount | Lower Limit | Other equity securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Measurement input	0.10
Sales restrictions discount | Lower Limit | Level 3 | Equity warrant asset, public portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Measurement input	0.100	0.100
Sales restrictions discount | Upper Limit | Other equity securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Measurement input	0.20
Sales restrictions discount | Upper Limit | Level 3 | Equity warrant asset, public portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Measurement input	0.200	0.200
Sales restrictions discount | Weighted Average | Level 3 | Equity warrant asset, public portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Measurement input	0.159	0.136
Volatility | Lower Limit | Level 3 | Equity warrant asset, public portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Measurement input	0.451	0.392
Volatility | Lower Limit | Level 3 | Equity warrant assets, private portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Measurement input	0.239	0.236
Volatility | Upper Limit | Level 3 | Equity warrant asset, public portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Measurement input	0.568	0.548
Volatility | Upper Limit | Level 3 | Equity warrant assets, private portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Measurement input	0.568	0.548
Volatility | Weighted Average | Level 3 | Equity warrant asset, public portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Measurement input	0.519	0.507
Volatility | Weighted Average | Level 3 | Equity warrant assets, private portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Measurement input	0.436	0.382
Risk-Free interest rate | Level 3 | Equity warrant asset, public portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Measurement input		0.019
Risk-Free interest rate | Lower Limit | Level 3 | Equity warrant asset, public portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Measurement input	0.003
Risk-Free interest rate | Lower Limit | Level 3 | Equity warrant assets, private portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Measurement input	0.0001	0.005
Risk-Free interest rate | Upper Limit | Level 3 | Equity warrant asset, public portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Measurement input	0.007
Risk-Free interest rate | Upper Limit | Level 3 | Equity warrant assets, private portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Measurement input	0.0069	0.019
Risk-Free interest rate | Weighted Average | Level 3 | Equity warrant asset, public portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Measurement input	0.006	0.019
Risk-Free interest rate | Weighted Average | Level 3 | Equity warrant assets, private portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Measurement input	0.002	0.016
Marketability discount | Level 3 | Equity warrant assets, private portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Measurement input	0.221	0.175
Marketability discount | Weighted Average | Level 3 | Equity warrant assets, private portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Measurement input	0.221	0.175
Remaining life assumption | Level 3 | Equity warrant assets, private portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Measurement input	0.450	0.450
Remaining life assumption | Weighted Average | Level 3 | Equity warrant assets, private portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Measurement input	0.450	0.450