Fair Value of Financial Instruments - Valuation Techniques Used to Measure Investments (Details) $ in Thousands	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Limited liability investments, at fair value	$ 19,654	$ 32,811
Real estate investments	10,662	10,662
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Limited liability investments, at fair value	3,374	3,263	$ 4,413	$ 4,392
Real estate investments	10,662	10,662	10,662	10,662
Stock-based compensation liabilities	$ 0	$ 0	$ 216	$ 249
Significant Unobservable Inputs (Level 3) | Minimum | Valuation multiples
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Limited liability investments, measurement input	3.1	3.1
Warrant liability, measurement input	6.0	6.0
Significant Unobservable Inputs (Level 3) | Minimum | Royalty rate | Relief from royalty
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Input Value(s)	0.0025
Significant Unobservable Inputs (Level 3) | Maximum | Valuation multiples
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Limited liability investments, measurement input	7.0	7.0
Significant Unobservable Inputs (Level 3) | Maximum | Royalty rate | Relief from royalty
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Input Value(s)	0.020