Investment Information - Limited partnership interests (Details) - USD ($) $ in Thousands		Jun. 30, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Maximum Exposure to Loss		$ 1,906,196	$ 1,848,679
Aggregate unfunded commitments		1,770,000	1,690,000
Equity method investments
Schedule of Equity Method Investments [Line Items]
Maximum Exposure to Loss	[1]	1,727,302	1,660,396
Aggregate unfunded commitments		1,440,000	1,360,000
Fair value option
Schedule of Equity Method Investments [Line Items]
Maximum Exposure to Loss	[2]	178,894	188,283
Aggregate unfunded commitments		$ 32,300	$ 41,700

[1] Aggregate unfunded commitments were $1.44 billion at June 30, 2020, compared to $1.36 billion at December 31, 2019.

[2] Aggregate unfunded commitments were $32.3 million at June 30, 2020, compared to $41.7 million at December 31, 2019.