Basis of Presentation and Summary of Significant Accounting Policies - Goodwill and Intangible Assets (Details) - USD ($)	9 Months Ended
	Sep. 30, 2024	Dec. 31, 2023
Business Acquisition
Goodwill	$ 46,062,000	$ 46,062,000
Indefinite-lived intangibles	7,500,000	7,500,000
Total goodwill and intangibles	53,562,000	53,562,000
Goodwill and intangible asset impairment	0
Surety
Business Acquisition
Goodwill	40,816,000	40,816,000
Casualty
Business Acquisition
Goodwill	$ 5,246,000	$ 5,246,000