Investment Information - Other investments (Details) - Fair value option - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Schedule Of Other Investments [Line Items]
Other investments	$ 2,169,897	$ 2,429,316
Term loan investments
Schedule Of Other Investments [Line Items]
Other investments	1,202,526	1,326,018
Lending
Schedule Of Other Investments [Line Items]
Other investments	575,623	602,841
Credit related funds
Schedule Of Other Investments [Line Items]
Other investments	98,121	123,020
Energy
Schedule Of Other Investments [Line Items]
Other investments	65,330	97,402
Investment grade fixed income
Schedule Of Other Investments [Line Items]
Other investments	114,784	151,594
Infrastructure
Schedule Of Other Investments [Line Items]
Other investments	60,579	61,786
Private equity
Schedule Of Other Investments [Line Items]
Other investments	34,983	49,376
Real estate
Schedule Of Other Investments [Line Items]
Other investments	$ 17,951	$ 17,279