Investments - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($) security	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Fair value of investments, assets managed on behalf of the trade capital providers | $	$ 55.9	$ 89.6
Debt securities, available-for-sale, term	3 years 3 months 14 days	2 years 9 months 21 days
Number of securities in an unrealized loss position, total | security	1,593
Number of securities in an unrealized loss position for less than one year | security	1,060
Number of securities in an unrealized loss position for a period of one year or greater | security	485
Change in allowance for credit losses on fixed maturity securities | $	$ (2.5)	$ 0.6	$ (39.9)
Gain (Loss) on Investments
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Change in allowance for credit losses on fixed maturity securities | $	$ 2.5	$ 0.6