Investments - Realized Investment Gains (Losses) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Gain (Loss) on Securities [Line Items]
Net investment gains (losses)	$ 2,469	$ (2,156)	$ (12,833)	$ 151,594
Fixed maturity securities
Gain (Loss) on Securities [Line Items]
Net investment gains (losses)	2,656	206	3,116	141,955
Equity securities
Gain (Loss) on Securities [Line Items]
Net investment gains (losses)	3,982	1,478	(3,670)	13,311
Short-term investments and other
Gain (Loss) on Securities [Line Items]
Net investment gains (losses)	$ (4,169)	$ (3,840)	$ (12,279)	$ (3,672)