Investments - Credit Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cumulative credit loss
Beginning of period	$ 1,529	$ 3,825
New credit losses	0	0
Increases to previously recognized credit losses	0	246
Losses related to securities sold or paid down during the period	0	(2,542)
End of period	$ 1,529	$ 1,529