Fair Value of Financial Instruments - Reconciliation of Fair Value of Recurring Level 3 Measurements (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Limited liability investments, at fair value:
Beginning balance			$ 26,015
Purchases			(824)	$ (119)
Net realized gains (losses)	$ 1,001	$ (414)	760	(17)
Ending balance	29,559		29,559
Real estate investments:
Beginning balance			10,662
Ending balance	10,662		10,662
Total assets	58,591		58,591		$ 52,024
Warrant liability:
Ending balance - liabilities	280		280
Significant Unobservable Inputs (Level 3)
Limited liability investments, at fair value:
Beginning balance	4,635	2,083	4,124	1,397
Purchases	72	307	746	1,285
Distributions received	(915)	(34)	(1,253)	(596)
Net realized gains (losses)	711	0	794	251
Change in fair value of limited liability investments, at fair value included in net loss	(933)	(26)	(841)	(7)
Ending balance	3,570	2,330	3,570	2,330
Unrealized (losses) gains recognized in net loss on limited liability investments, at fair value held at end of period	(909)	27	(793)	65
Real estate investments:
Beginning balance	10,662	10,662	10,662	10,662
Change in fair value of real estate investments included in net loss	0	0	0	0
Ending balance	10,662	10,662	10,662	10,662
Unrealized gains recognized in net loss on real estate investments held at end of period	0	0	0	0
Total assets	14,232	12,992	14,232	12,992	$ 14,786
Warrant liability:
Beginning balance	307	0	0	0
Issuance of warrants	0	0	361	0
Change in fair value of warrant liability included in net loss	(27)	0	(81)	0
Ending balance - liabilities	280	0	280	0
Unrealized gains recognized in net loss on warrant liability held at end of period	$ (27)	$ 0	$ (81)	$ 0