Investment Information - Limited partnership interests (Details) - USD ($) $ in Thousands		Sep. 30, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Maximum Exposure to Loss		$ 2,064,111	$ 1,848,679
Aggregate unfunded commitments		1,910,000	1,690,000
Equity method investments
Schedule of Equity Method Investments [Line Items]
Maximum Exposure to Loss	[1]	1,883,702	1,660,396
Aggregate unfunded commitments		1,590,000	1,360,000
Fair value option
Schedule of Equity Method Investments [Line Items]
Maximum Exposure to Loss	[2]	180,409	188,283
Aggregate unfunded commitments		$ 36,700	$ 41,700

[1] Aggregate unfunded commitments were $1.59 billion at September 30, 2020, compared to $1.36 billion at December 31, 2019.

[2] Aggregate unfunded commitments were $36.7 million at September 30, 2020, compared to $41.7 million at December 31, 2019.