Investment Information - Limited partnership interests (Details) - USD ($) $ in Thousands		Sep. 30, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Maximum Exposure to Loss		$ 1,765,018	$ 1,656,189
Aggregate unfunded commitments		1,900,000	1,770,000
Equity method investments
Schedule of Equity Method Investments [Line Items]
Maximum Exposure to Loss	[1]	1,575,832	1,493,791
Aggregate unfunded commitments		1,440,000	1,220,000
Fair value option
Schedule of Equity Method Investments [Line Items]
Maximum Exposure to Loss	[2]	189,186	162,398
Aggregate unfunded commitments		$ 51,100	$ 117,500

[1] Aggregate unfunded commitments were $1.44 billion at September 30, 2019, compared to $1.22 billion at December 31, 2018.

[2] Aggregate unfunded commitments were $51.1 million at September 30, 2019, compared to $117.5 million at December 31, 2018.