Plant Closure and Divestitures - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended
	Feb. 28, 2021	Mar. 31, 2021	Mar. 31, 2020
Restructuring Cost and Reserve [Line Items]
Gain on sale		$ 7.5	$ 0.0
Coal Tar Distillation [Member] | West Virginia [Member]
Restructuring Cost and Reserve [Line Items]
Gain on sale	$ 5.7
Cash proceed from sale	$ 2.6
Coal Tar Distillation [Member] | Pennsylvania [Member]
Restructuring Cost and Reserve [Line Items]
Gain on sale		$ 1.8