Bank Line of Credit (Details) - Revolving Line of Credit - USD ($)	Dec. 31, 2024	Dec. 31, 2023
Bank line of credit
Maximum borrowing capacity under the bank revolving line of credit	$ 100,000,000
Maximum letter of credit sublimit under the bank revolving line of credit	25,000,000
Available borrowing capacity under the bank revolving line of credit, due to outstanding letters of credit	99,200,000
Outstanding amount of letters of credit sublimit under the bank revolving line of credit	800,000
Available amount of letters of credit sublimit under the bank revolving line of credit	24,200,000
Borrowings outstanding under the bank revolving line of credit		$ 0
Security owned and pledged as collateral, associated liabilities, fair value	$ 118,600,000