Investment Information - Limited partnership interests (Details) - USD ($) $ in Thousands		Dec. 31, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Maximum Exposure to Loss		$ 1,848,679	$ 1,656,189
Aggregate commitments		1,690,000	1,770,000
Equity method investments
Schedule of Equity Method Investments [Line Items]
Maximum Exposure to Loss	[1]	1,660,396	1,493,791
Aggregate commitments		1,360,000	1,220,000
Fair value option
Schedule of Equity Method Investments [Line Items]
Maximum Exposure to Loss	[2]	188,283	162,398
Aggregate commitments		$ 41,700	$ 117,500

[1] Aggregate unfunded commitments were $1.36 billion at December 31, 2019, compared to $1.22 billion at December 31, 2018.

[2] Aggregate unfunded commitments were $41.7 million at December 31, 2019, compared to $117.5 million at December 31, 2018.