Investments - Realized Investment Gains (Losses) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Gain (Loss) on Securities [Line Items]
Net investment gains (losses)	$ (18,464)	$ 7,417
Fixed maturity securities
Gain (Loss) on Securities [Line Items]
Net investment gains (losses)	1,102	201
Equity securities
Gain (Loss) on Securities [Line Items]
Net investment gains (losses)	(14,723)	7,907
Short-term investments and other
Gain (Loss) on Securities [Line Items]
Net investment gains (losses)	$ (4,843)	$ (691)