Investment Information - Fair value option (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	$ 3,310,517	$ 3,663,477
Fixed maturities
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	734,694	754,452
Other investments
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	2,091,417	2,429,316
Short-term investments
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	396,409	377,014
Equity securities
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	$ 87,997	$ 102,695