Business Segments - Segment Reporting, Reconciliation of Revenues, Operating Income and Assets (Parenthetical) (Detail) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Strategic Capital [Member] \| Europe [Member]
Segment Reporting Information [Line Items]
Goodwill	$ 25.3	$ 25.3

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant