Investments - Summary of Fair Value, Including Financial Guarantee, and Weighted-Average Underlying Rating, Excluding Financial Guarantee, of Insured Securities (Phantom) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Investment [Line Items]
Investment expense	$ 2	$ (90)
Net investment income	2,815	3,640
Fixed Income Investments [Member]
Investment [Line Items]
Gross Investment Income, Operating	1,400	1,170
Short-Term [Member]
Investment [Line Items]
Gross Investment Income, Operating	1,457	2,590
Other Investments [Member]
Investment [Line Items]
Gross Investment Income, Operating	$ (79)	$ (30)