Investments, Investments Temporarily Impaired (Details) $ in Thousands	Jun. 30, 2020 USD ($) Investment
Temporarily Impaired Investments [Abstract]
Number of investments | Investment	78
Estimated fair value, less than 12 months of temporary impairment	$ 249,679
Unrealized losses, less than 12 months of temporary impairment	(188)
Estimated fair value, more than 12 months of temporary impairment	26,997
Unrealized losses, more than 12 months of temporary impairment	(4)
Estimated fair value, total temporary impairment	276,676
Unrealized losses, total temporary impairment	$ (192)
Corporate Debt Securities [Member]
Temporarily Impaired Investments [Abstract]
Number of investments | Investment	37
Estimated fair value, less than 12 months of temporary impairment	$ 87,460
Unrealized losses, less than 12 months of temporary impairment	(138)
Estimated fair value, more than 12 months of temporary impairment	0
Unrealized losses, more than 12 months of temporary impairment	0
Estimated fair value, total temporary impairment	87,460
Unrealized losses, total temporary impairment	$ (138)
Debt Securities issued by U.S. Government Agencies [Member]
Temporarily Impaired Investments [Abstract]
Number of investments | Investment	10
Estimated fair value, less than 12 months of temporary impairment	$ 44,389
Unrealized losses, less than 12 months of temporary impairment	(33)
Estimated fair value, more than 12 months of temporary impairment	26,997
Unrealized losses, more than 12 months of temporary impairment	(4)
Estimated fair value, total temporary impairment	71,386
Unrealized losses, total temporary impairment	$ (37)
Debt Securities issued by the U.S. Treasury [Member]
Temporarily Impaired Investments [Abstract]
Number of investments | Investment	9
Estimated fair value, less than 12 months of temporary impairment	$ 110,067
Unrealized losses, less than 12 months of temporary impairment	(11)
Estimated fair value, more than 12 months of temporary impairment	0
Unrealized losses, more than 12 months of temporary impairment	0
Estimated fair value, total temporary impairment	110,067
Unrealized losses, total temporary impairment	$ (11)
Debt Securities issued by States of the U.S. and Political Subdivisions of the States [Member]
Temporarily Impaired Investments [Abstract]
Number of investments | Investment	22
Estimated fair value, less than 12 months of temporary impairment	$ 7,763
Unrealized losses, less than 12 months of temporary impairment	(6)
Estimated fair value, more than 12 months of temporary impairment	0
Unrealized losses, more than 12 months of temporary impairment	0
Estimated fair value, total temporary impairment	7,763
Unrealized losses, total temporary impairment	$ (6)