Fair Value of Financial Instruments - Reconciliation of Fair Value of Recurring Level 3 Measurements (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Limited liability investments, at fair value:
Beginning balance			$ 26,015
Purchases			(249)	$ (95)
Net realized (losses) gains	$ (556)	$ 132	(241)	397
Ending balance	33,047		33,047
Real estate investments:
Beginning balance			10,662
Ending balance	10,662		10,662
Total assets	65,747		65,747		$ 52,024
Warrant liability:
Ending balance - liabilities	307		307
Significant Unobservable Inputs (Level 3)
Limited liability investments, at fair value:
Beginning balance	4,060	1,634	4,124	1,397
Purchases	599	504	674	978
Distributions received	(14)	(70)	(338)	(562)
Net realized (losses) gains	14	0	83	251
Change in fair value of limited liability investments, at fair value included in net income (loss)	(24)	15	92	19
Ending balance	4,635	2,083	4,635	2,083
Unrealized gains recognized in net (loss) income on limited liability investments, at fair value held at end of period	0	15	116	38
Real estate investments:
Beginning balance	10,662	10,662	10,662	10,662
Change in fair value of real estate investments included in net income (loss)	0	0	0	0
Ending balance	10,662	10,662	10,662	10,662
Unrealized gains recognized in net (loss) income on real estate investments held at end of period	0	0	0	0
Total assets	15,297	12,745	15,297	12,745	$ 14,786
Warrant liability:
Beginning balance	317	0	0	0
Issuance of warrants	0	0	361	0
Change in fair value of warrant liability included in net (loss) income	(10)	0	(54)	0
Ending balance - liabilities	307	0	307	0
Unrealized gains recognized in net (loss) income on warrant liability held at end of period	$ (10)	$ 0	$ (54)	$ 0