Investments - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($) security	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)
Investments, Debt and Equity Securities [Abstract]
Fair value of investments, assets managed on behalf of the trade capital providers | $	$ 120.9		$ 158.6
Number of securities in an unrealized loss position, total | security	4,842
Number of securities in an unrealized loss position for less than one year | security	2,480
Number of securities in an unrealized loss position for a period of one year or greater | security	194
Provision for expected credit losses | $	$ 24.7
Impairment losses | $	$ 0.0	$ 4.3