Regulatory Requirements (Detail) $ in Millions	Sep. 30, 2023 USD ($)
Broker-Dealer, Net Capital Requirement, SEC Regulation [Abstract]
Net assets held by regulated subsidiaries	$ 703.1
Amount of capital in excess of aggregate regulatory requirements	$ 372.5

Amount of total risk-based capital exceeding minimum required for capital adequacy as defined by regulatory framework.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480696/942-505-50-1

Name:	us-gaap_ExcessCapital
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant