Investments - Net Investment Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Schedule of Investments [Line Items]
Investment income	$ 219,339	$ 171,843	$ 160,598
Investment expenses	(4,599)	(4,367)	(4,160)
Investment income, net of expenses	214,740	167,476	156,438
Total fixed income securities
Schedule of Investments [Line Items]
Investment income	202,655	166,306	160,030
Equity securities
Schedule of Investments [Line Items]
Investment income	529	437	471
Cash equivalents
Schedule of Investments [Line Items]
Investment income	16,111	5,049	75
Other
Schedule of Investments [Line Items]
Investment income	$ 44	$ 51	$ 22