Investments - Contractual Maturities of Debt Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Cost
Due within one year	$ 81,637	$ 65,039
Due after one year through five years	47,212	62,293
Due after five years through ten years	51,892	50,606
Due after ten years	173,794	100,092
Total	354,535	278,030
Fair Value
Due within one year	81,914	63,925
Due after one year through five years	48,188	61,924
Due after five years through ten years	54,184	49,855
Due after ten years	177,849	99,089
Total	$ 362,135	$ 274,793