Investment Information - Equity method investments (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Investments accounted for using the equity method	$ 1,676,055	$ 1,660,396
Credit related funds
Schedule of Equity Method Investments [Line Items]
Investments accounted for using the equity method	421,943	428,437
Equity securities
Schedule of Equity Method Investments [Line Items]
Investments accounted for using the equity method	256,249	293,686
Real estate
Schedule of Equity Method Investments [Line Items]
Investments accounted for using the equity method	254,957	246,851
Lending
Schedule of Equity Method Investments [Line Items]
Investments accounted for using the equity method	194,132	202,690
Private equity
Schedule of Equity Method Investments [Line Items]
Investments accounted for using the equity method	154,322	144,983
Infrastructure
Schedule of Equity Method Investments [Line Items]
Investments accounted for using the equity method	283,147	235,033
Energy
Schedule of Equity Method Investments [Line Items]
Investments accounted for using the equity method	$ 111,305	$ 108,716