Employee Benefit Plans (Narrative) (Detail) - Unfunded Supplemental Benefit Plans $ in Millions	9 Months Ended
Sep. 30, 2021 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Contribution for pension obligation	$ 10.8
Cash contribution to plans during the remainder	$ 4.6

Amount of contribution received by defined benefit plan from employer which increases plan assets.

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Name:	us-gaap_DefinedBenefitPlanContributionsByEmployer
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration