Investment Information - Equity method investments (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Investments accounted for using the equity method	$ 1,575,832	$ 1,493,791
Credit related funds
Schedule of Equity Method Investments [Line Items]
Investments accounted for using the equity method	428,353	429,402
Equity securities
Schedule of Equity Method Investments [Line Items]
Investments accounted for using the equity method	284,465	375,273
Real estate
Schedule of Equity Method Investments [Line Items]
Investments accounted for using the equity method	265,502	232,647
Lending
Schedule of Equity Method Investments [Line Items]
Investments accounted for using the equity method	200,112	125,041
Private equity
Schedule of Equity Method Investments [Line Items]
Investments accounted for using the equity method	141,343	114,019
Infrastructure
Schedule of Equity Method Investments [Line Items]
Investments accounted for using the equity method	149,005	113,748
Energy
Schedule of Equity Method Investments [Line Items]
Investments accounted for using the equity method	$ 107,052	$ 103,661