Investments - Temporarily Impaired Investments (Details) $ in Thousands	Jun. 30, 2025 USD ($) Investment
Investments [Abstract]
Number of investments (in Investment) | Investment	379
Less than 12 months of temporary impairment	$ 1,124,924
Less than 12 months of temporary impairment	(1,310)
More than 12 months of temporary impairment	14,998
More than 12 months of temporary impairment	(56)
Total temporary impairment	1,139,922
Total temporary impairment	$ (1,366)
Corporate Debt Securities [Member]
Investments [Abstract]
Number of investments (in Investment) | Investment	252
Less than 12 months of temporary impairment	$ 544,205
Less than 12 months of temporary impairment	(728)
More than 12 months of temporary impairment	1,958
More than 12 months of temporary impairment	(6)
Total temporary impairment	546,163
Total temporary impairment	$ (734)
Debt Securities Issued by U.S. Government Agencies [Member]
Investments [Abstract]
Number of investments (in Investment) | Investment	44
Less than 12 months of temporary impairment	$ 87,403
Less than 12 months of temporary impairment	(140)
More than 12 months of temporary impairment	0
More than 12 months of temporary impairment	0
Total temporary impairment	87,403
Total temporary impairment	$ (140)
Debt Securities Issued by the U.S. Treasury [Member]
Investments [Abstract]
Number of investments (in Investment) | Investment	76
Less than 12 months of temporary impairment	$ 488,942
Less than 12 months of temporary impairment	(440)
More than 12 months of temporary impairment	13,040
More than 12 months of temporary impairment	(50)
Total temporary impairment	501,982
Total temporary impairment	$ (490)
Debt Securities Issued by States of the U.S. and Political Subdivisions of the States [Member]
Investments [Abstract]
Number of investments (in Investment) | Investment	6
Less than 12 months of temporary impairment	$ 3,677
Less than 12 months of temporary impairment	(1)
More than 12 months of temporary impairment	0
More than 12 months of temporary impairment	0
Total temporary impairment	3,677
Total temporary impairment	$ (1)
Other Municipal Debt Securities [Member]
Investments [Abstract]
Number of investments (in Investment) | Investment	1
Less than 12 months of temporary impairment	$ 697
Less than 12 months of temporary impairment	(1)
More than 12 months of temporary impairment	0
More than 12 months of temporary impairment	0
Total temporary impairment	697
Total temporary impairment	$ (1)