Available-For-Sale Securities (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Available-for-Sale Securities [Line Items]
Fair value of securities pledged as collateral	$ 101.5	$ 53.9
Securities delivered for repurchase agreements	21.5	17.8
Fair value investments	$ 211.7	$ 235.5
Fair value as a percentage of available-for-sale investment portfolio	99.00%	100.00%
Unrealized loss on securities	$ 50.0	$ 40.7