Agreements and Transactions with Related Parties - Related Party Income (Details) - Affiliated Entity - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Related Party Transaction
Distributions of Available Cash	$ 7,225	$ 21,489	$ 46,609
Interest income on deferred acquisition fees and loans to affiliates	369	2,237	2,055
Total deferred revenue earned	38,916	83,629	155,271
Asset management revenue
Related Party Transaction
Gross contract revenue	21,973	39,132	63,556
Reimbursable costs from affiliates
Related Party Transaction
Gross contract revenue	8,855	16,547	21,925
Structuring and other advisory revenue
Related Party Transaction
Gross contract revenue	$ 494	$ 4,224	$ 21,126