Revenues - Management Fees and Incentive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Incentive income
Disaggregation of Revenue [Line Items]
Investment management revenues	$ 9,322	$ 53,198
Management fees
Disaggregation of Revenue [Line Items]
Investment management revenues	66,953	63,623
Multi-strategy funds | Incentive income
Disaggregation of Revenue [Line Items]
Investment management revenues	1,824	14,984
Multi-strategy funds | Management fees
Disaggregation of Revenue [Line Items]
Investment management revenues	32,373	34,381
Opportunistic credit funds | Incentive income
Disaggregation of Revenue [Line Items]
Investment management revenues	4,670	30,920
Opportunistic credit funds | Management fees
Disaggregation of Revenue [Line Items]
Investment management revenues	9,563	10,435
Institutional Credit Strategies | Incentive income
Disaggregation of Revenue [Line Items]
Investment management revenues	0	0
Institutional Credit Strategies | Management fees
Disaggregation of Revenue [Line Items]
Investment management revenues	15,266	13,723
Real estate funds | Incentive income
Disaggregation of Revenue [Line Items]
Investment management revenues	2,828	7,294
Real estate funds | Management fees
Disaggregation of Revenue [Line Items]
Investment management revenues	9,743	4,832
Other | Incentive income
Disaggregation of Revenue [Line Items]
Investment management revenues	0	0
Other | Management fees
Disaggregation of Revenue [Line Items]
Investment management revenues	$ 8	$ 252