Segment Information - Schedule of Segment Revenues for Significant Product Lines (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Net sales	$ 401.9	$ 376.9
Railroad and Utility Products and Services [Member]
Segment Reporting Information [Line Items]
Net sales	190.0	166.1
Railroad and Utility Products and Services [Member] | Railroad Treated Products [Member]
Segment Reporting Information [Line Items]
Net sales	112.0	88.6
Railroad and Utility Products and Services [Member] | Utility Poles [Member]
Segment Reporting Information [Line Items]
Net sales	61.9	54.5
Railroad and Utility Products and Services [Member] | Rail Joints [Member]
Segment Reporting Information [Line Items]
Net sales	6.4	8.3
Railroad and Utility Products and Services [Member] | Railroad Infrastructure Services [Member]
Segment Reporting Information [Line Items]
Net sales	6.0	8.8
Railroad and Utility Products and Services [Member] | Other Products [Member]
Segment Reporting Information [Line Items]
Net sales	3.7	5.9
Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales	111.4	99.0
Performance Chemicals [Member] | Other Products [Member]
Segment Reporting Information [Line Items]
Net sales	3.8	2.6
Performance Chemicals [Member] | Wood Preservative Products [Member]
Segment Reporting Information [Line Items]
Net sales	107.6	96.4
Carbon Materials and Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales	100.5	111.8
Carbon Materials and Chemicals [Member] | Other Products [Member]
Segment Reporting Information [Line Items]
Net sales	6.6	5.8
Carbon Materials and Chemicals [Member] | Pitch and Related Products [Member]
Segment Reporting Information [Line Items]
Net sales	50.2	62.8
Carbon Materials and Chemicals [Member] | Phthalic Anhydride and Other Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales	23.5	21.0
Carbon Materials and Chemicals [Member] | Creosote and Distillates [Member]
Segment Reporting Information [Line Items]
Net sales	15.2	15.9
Carbon Materials and Chemicals [Member] | Naphthalene [Member]
Segment Reporting Information [Line Items]
Net sales	$ 5.0	$ 6.4