Revenues - Management Fees and Incentive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Incentive income
Disaggregation of Revenue [Line Items]
Investment management revenues	$ 38,238	$ 34,757	$ 47,560	$ 87,955
Management fees
Disaggregation of Revenue [Line Items]
Investment management revenues	60,383	61,400	127,336	125,023
Multi-strategy funds | Incentive income
Disaggregation of Revenue [Line Items]
Investment management revenues	34,540	30,800	36,364	45,784
Multi-strategy funds | Management fees
Disaggregation of Revenue [Line Items]
Investment management revenues	29,214	34,219	61,587	68,600
Opportunistic credit funds | Incentive income
Disaggregation of Revenue [Line Items]
Investment management revenues	2,750	2,069	7,420	32,989
Opportunistic credit funds | Management fees
Disaggregation of Revenue [Line Items]
Investment management revenues	11,233	10,704	20,796	21,139
Institutional Credit Strategies | Incentive income
Disaggregation of Revenue [Line Items]
Investment management revenues	0	0	0	0
Institutional Credit Strategies | Management fees
Disaggregation of Revenue [Line Items]
Investment management revenues	8,085	13,848	23,351	27,571
Real estate funds | Incentive income
Disaggregation of Revenue [Line Items]
Investment management revenues	948	1,888	3,776	9,182
Real estate funds | Management fees
Disaggregation of Revenue [Line Items]
Investment management revenues	11,851	2,417	21,594	7,249
Other | Incentive income
Disaggregation of Revenue [Line Items]
Investment management revenues	0	0	0	0
Other | Management fees
Disaggregation of Revenue [Line Items]
Investment management revenues	$ 0	$ 212	$ 8	$ 464