Fair Value of Financial Instruments - Quantitative Information About Significant Unobservable Inputs (Details) - Level 3 $ in Thousands	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Equity warrant asset, public portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair value	$ 318	$ 346
Equity warrant assets, private portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair value	$ 149,540	$ 160,692
Volatility | Equity warrant asset, public portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Weighted Average	0.559	0.507
Volatility | Equity warrant assets, private portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Weighted Average	0.411	0.382
Risk-Free interest rate | Equity warrant asset, public portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Weighted Average	0.007	0.019
Risk-Free interest rate | Equity warrant assets, private portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Weighted Average	0.003	0.016
Sales restrictions discount | Equity warrant asset, public portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Weighted Average	0.146	0.136
Marketability discount | Equity warrant assets, private portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Weighted Average	0.250	0.175
Remaining life assumption | Equity warrant assets, private portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Weighted Average	0.450	0.450
Unconsolidated venture capital and private equity fund investments
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair value	$ 134	$ 134