Investments - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($) security	Mar. 31, 2021 USD ($)	Dec. 31, 2021 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 | $	$ 71.2		$ 89.6
Number of securities in an unrealized loss position, total | security	5,203
Number of securities in an unrealized loss position for less than one year | security	1,080
Number of securities in an unrealized loss position for a period of one year or greater | security	208
Credit losses on fixed maturities | $	$ 1.0	$ 1.1
Gain (Loss) on Investments
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Credit losses on fixed maturities | $	$ 1.0	$ 1.1