Revenues - Management Fees and Incentive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Incentive income
Disaggregation of Revenue [Line Items]
Investment management revenues	$ 321,621	$ 202,896	$ 528,000
Management fees
Disaggregation of Revenue [Line Items]
Investment management revenues	253,011	281,862	319,458
Multi-strategy funds | Incentive income
Disaggregation of Revenue [Line Items]
Investment management revenues	240,517	71,972	409,823
Multi-strategy funds | Management fees
Disaggregation of Revenue [Line Items]
Investment management revenues	134,404	168,902	214,116
Opportunistic credit funds | Incentive income
Disaggregation of Revenue [Line Items]
Investment management revenues	48,526	89,182	99,308
Opportunistic credit funds | Management fees
Disaggregation of Revenue [Line Items]
Investment management revenues	43,729	41,035	44,753
Institutional Credit Strategies | Incentive income
Disaggregation of Revenue [Line Items]
Investment management revenues	0	0	0
Institutional Credit Strategies | Management fees
Disaggregation of Revenue [Line Items]
Investment management revenues	57,877	50,212	35,381
Real estate funds | Incentive income
Disaggregation of Revenue [Line Items]
Investment management revenues	32,578	40,811	7,603
Real estate funds | Management fees
Disaggregation of Revenue [Line Items]
Investment management revenues	16,111	19,307	21,027
Other | Incentive income
Disaggregation of Revenue [Line Items]
Investment management revenues	0	931	11,266
Other | Management fees
Disaggregation of Revenue [Line Items]
Investment management revenues	$ 890	$ 2,406	$ 4,181