Investments - Realized Investment Gains (Losses) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Gain (Loss) on Securities [Line Items]
Net investment gains (losses)	$ (12,543)	$ (3,406)	$ 4,123
Fixed maturity securities
Gain (Loss) on Securities [Line Items]
Net investment gains (losses)	(5,713)	(8,867)	5,784
Equity securities
Gain (Loss) on Securities [Line Items]
Net investment gains (losses)	(10,649)	4,003	(608)
Short-term and other investments
Gain (Loss) on Securities [Line Items]
Net investment gains (losses)	$ 3,819	$ 1,458	$ (1,053)