Other Nonoperating (Income) and Expenses, Net - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Component of Other Operating Income and Expense [Line Items]
Out of period expenses		$ 15.7
Other Nonoperating (Income) and Expenses, Net
Component of Other Operating Income and Expense [Line Items]
Third-party railroad track maintenance expense	$ 11.4
Reduction in pension expense	8.1
Out of period expenses	15.7
Out of period expense net of tax	$ 12.0