Investments, Investments Temporarily Impaired (Details) $ in Thousands	Dec. 31, 2021 USD ($) Investment
Temporarily Impaired Investments [Abstract]
Number of investments | Investment	727
Estimated fair value, less than 12 months of temporary impairment	$ 934,791
Unrealized losses, less than 12 months of temporary impairment	$ (4,311)
Corporate Debt Securities [Member]
Temporarily Impaired Investments [Abstract]
Number of investments | Investment	272
Estimated fair value, less than 12 months of temporary impairment	$ 552,966
Unrealized losses, less than 12 months of temporary impairment	$ (2,870)
Debt Securities Issued by U.S. Government Agencies [Member]
Temporarily Impaired Investments [Abstract]
Number of investments | Investment	15
Estimated fair value, less than 12 months of temporary impairment	$ 114,338
Unrealized losses, less than 12 months of temporary impairment	$ (579)
Debt Securities Issued by the U.S. Treasury [Member]
Temporarily Impaired Investments [Abstract]
Number of investments | Investment	13
Estimated fair value, less than 12 months of temporary impairment	$ 134,987
Unrealized losses, less than 12 months of temporary impairment	$ (564)
Debt Securities Issued by States of the U.S. and Political Subdivisions of the States [Member]
Temporarily Impaired Investments [Abstract]
Number of investments | Investment	425
Estimated fair value, less than 12 months of temporary impairment	$ 126,401
Unrealized losses, less than 12 months of temporary impairment	$ (261)
Other Municipal Debt Securities [Member]
Temporarily Impaired Investments [Abstract]
Number of investments | Investment	2
Estimated fair value, less than 12 months of temporary impairment	$ 6,099
Unrealized losses, less than 12 months of temporary impairment	$ (37)