Regulatory Requirements (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($)
Broker-Dealer, Net Capital Requirement, SEC Regulation [Abstract]
Minimum period required for financial resources to cover operating costs	1 year
Minimum period required for cash or highly liquid securities to cover operating costs	6 months
Net assets held by regulated subsidiaries	$ 667.2
Amount of capital in excess of aggregate regulatory requirements	$ 326.9