Investments - Realized Investment Gains (Losses) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Gain (Loss) on Securities [Line Items]
Net investment gains (losses)	$ 3,162	$ 146,333	$ (15,302)	$ 153,750
Fixed maturity securities
Gain (Loss) on Securities [Line Items]
Net investment gains (losses)	(642)	141,548	460	141,749
Equity securities
Gain (Loss) on Securities [Line Items]
Net investment gains (losses)	7,071	3,926	(7,652)	11,833
Short-term investments and other
Gain (Loss) on Securities [Line Items]
Net investment gains (losses)	$ (3,267)	$ 859	$ (8,110)	$ 168