Investments -Schedule of Net Investment Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Net Investment Income [Line Items]
Net investment income earned	$ 108,642	$ 97,696	$ 216,491	$ 189,202
Fixed income securities
Net Investment Income [Line Items]
Net investment income earned	93,935	83,916	188,037	164,003
Commercial mortgage loans ("CMLs")
Net Investment Income [Line Items]
Net investment income earned	3,145	2,199	5,939	4,164
Equity securities
Net Investment Income [Line Items]
Net investment income earned	1,877	2,236	6,785	3,441
Short-term investments
Net Investment Income [Line Items]
Net investment income earned	4,680	2,892	8,199	7,542
Alternative investments
Net Investment Income [Line Items]
Net investment income earned	10,517	11,396	17,398	19,164
Other investments
Net Investment Income [Line Items]
Net investment income earned	118	188	381	231
Investment expenses
Net Investment Income [Line Items]
Investment expenses	$ (5,630)	$ (5,131)	$ (10,248)	$ (9,343)