Investments, Investments Temporarily Impaired (Details) $ in Thousands	Dec. 31, 2020 USD ($) Investment
Temporarily Impaired Investments [Abstract]
Number of investments | Investment	226
Estimated fair value, less than 12 months of temporary impairment	$ 284,148
Unrealized losses, less than 12 months of temporary impairment	$ (140)
Corporate Debt Securities [Member]
Temporarily Impaired Investments [Abstract]
Number of investments | Investment	54
Estimated fair value, less than 12 months of temporary impairment	$ 121,162
Unrealized losses, less than 12 months of temporary impairment	$ (81)
Debt Securities issued by U.S. Government Agencies [Member]
Temporarily Impaired Investments [Abstract]
Number of investments | Investment	2
Estimated fair value, less than 12 months of temporary impairment	$ 29,988
Unrealized losses, less than 12 months of temporary impairment	$ (11)
Debt Securities issued by the U.S. Treasury [Member]
Temporarily Impaired Investments [Abstract]
Number of investments | Investment	8
Estimated fair value, less than 12 months of temporary impairment	$ 76,941
Unrealized losses, less than 12 months of temporary impairment	$ (13)
Debt Securities issued by States of the U.S. and Political Subdivisions of the States [Member]
Temporarily Impaired Investments [Abstract]
Number of investments | Investment	160
Estimated fair value, less than 12 months of temporary impairment	$ 49,832
Unrealized losses, less than 12 months of temporary impairment	$ (28)
Other Municipal Debt Securities [Member]
Temporarily Impaired Investments [Abstract]
Number of investments | Investment	2
Estimated fair value, less than 12 months of temporary impairment	$ 6,225
Unrealized losses, less than 12 months of temporary impairment	$ (7)