Agreements and Transactions with Related Parties - Related Party Income (Details) - Affiliated Entity - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Related Party Transaction
Distributions of available cash	$ 2,029	$ 3,765	$ 3,945	$ 9,450
Interest income on deferred acquisition fees and loans to affiliates	83	571	360	1,091
Revenue from related parties	8,995	18,005	25,601	40,328
Asset management revenue
Related Party Transaction
Gross contract revenue	4,472	9,790	14,361	19,522
Reimbursable costs from affiliates
Related Party Transaction
Gross contract revenue	2,411	3,821	6,441	7,689
Structuring and other advisory revenue
Related Party Transaction
Gross contract revenue	$ 0	$ 58	$ 494	$ 2,576