Other Nonoperating (Income) and Expenses, Net - Additional Information (Detail) - Other Nonoperating (Income) and Expense, Net $ in Millions	9 Months Ended
Sep. 30, 2020 USD ($)
Component Of Other Income And Expense [Line Items]
Third-party railroad track maintenance expense	$ 5.6
Reduction in pension expense	8.9
Out of period expense	15.7
Out of period expense net of tax	$ 12.0

Amount of expense (reversal of expense) for net periodic benefit cost components, excluding service cost component, of defined benefit plan. Amount includes, but is not limited to, interest cost, expected (return) loss on plan asset, amortization of prior service cost (credit), amortization of (gain) loss, amortization of transition (asset) obligation, settlement (gain) loss, curtailment (gain) loss and certain termination benefits.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 45
-Paragraph 3A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109237824&loc=SL108413299-114919

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