Investments - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) security	Dec. 31, 2020 USD ($)	Dec. 31, 2019 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 | $	$ 89.6	$ 140.3
Number of securities in an unrealized loss position, total | security	5,207
Number of securities in an unrealized loss position for less than one year | security	697
Number of securities in an unrealized loss position for a period of one year or greater | security	82
Credit impairment losses | $	$ (0.6)	39.9	$ 0.0
Gain (Loss) on Investments
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Credit impairment losses | $	$ 0.6	$ (39.9)