Investment Information - Other investments (Details) - Fair value option - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Schedule Of Other Investments [Line Items]
Other investments	$ 2,440,120	$ 2,311,939
Term loan investments
Schedule Of Other Investments [Line Items]
Other investments	1,330,886	1,282,287
Other investments par	1,434,328	1,369,216
Lending
Schedule Of Other Investments [Line Items]
Other investments	624,699	524,112
Credit related funds
Schedule Of Other Investments [Line Items]
Other investments	165,444	202,123
Energy
Schedule Of Other Investments [Line Items]
Other investments	113,791	117,509
Investment grade fixed income
Schedule Of Other Investments [Line Items]
Other investments	83,649	101,902
Infrastructure
Schedule Of Other Investments [Line Items]
Other investments	49,602	45,371
Private equity
Schedule Of Other Investments [Line Items]
Other investments	54,609	24,383
Real estate
Schedule Of Other Investments [Line Items]
Other investments	$ 17,440	$ 14,252