Investments - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2023 USD ($) security	Mar. 31, 2022 USD ($)	Dec. 31, 2022 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 | $	$ 0.0		$ 55.9
Number of securities in an unrealized loss position, total | security	1,548
Number of securities in an unrealized loss position for less than one year | security	479
Number of securities in an unrealized loss position for a period of one year or greater | security	1,045
Credit losses on fixed maturities | $	$ 0.1	$ 1.0
Gain (Loss) on Investments
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Credit losses on fixed maturities | $	$ 0.1	$ 1.0