Borrowing Arrangements - Bank Line of Credit (Details) - Revolving Line of Credit $ in Millions	Dec. 31, 2022 USD ($)
Bank line of credit
Maximum borrowing capacity under the bank revolving line of credit	$ 100.0
Maximum letter of credit sublimit under the bank revolving line of credit	25.0
Available borrowing capacity under the bank revolving line of credit, due to outstanding letters of credit	99.1
Outstanding amount of letters of credit sublimit under the bank revolving line of credit	0.9
Available amount of letters of credit sublimit under the bank revolving line of credit	24.1
Security owned and pledged as collateral, associated liabilities, fair value	$ 114.6