Fair Value of Financial Instruments - Valuation Techniques Used to Measure Investments (Details) $ in Thousands	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Limited liability investments, at fair value	$ 30,986	$ 29,078
Real estate investments	10,662	10,662
Warrant liability	216	249
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Limited liability investments, at fair value	4,413	4,392	$ 4,060	$ 4,124
Real estate investments	10,662	10,662	10,662	10,662
Warrant liability	$ 216	$ 249	$ 317	$ 0
Significant Unobservable Inputs (Level 3) | Cap rates
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate investments, measurement input	0.075	0.075
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) | 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