Agreements and Transactions with Related Parties - Related Party Income (Details) - Affiliated Entity - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Related Party Transaction
Distributions of available cash	$ 1,168	$ 5,480	$ 5,113	$ 14,930
Interest income on deferred acquisition fees and loans to affiliates	0	636	360	1,727
Revenue from related parties	6,192	21,367	31,793	61,695
Asset management revenue
Related Party Transaction
Gross contract revenue	3,748	9,878	18,109	29,400
Reimbursable costs from affiliates
Related Party Transaction
Gross contract revenue	1,276	4,786	7,717	12,475
Structuring and other advisory revenue
Related Party Transaction
Gross contract revenue	$ 0	$ 587	$ 494	$ 3,163