Segment Information - Summary of Tangible and Intangible Assets by Segments (Detail) - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Asset Reconciling Item [Line Items]
Assets		$ 1,598.6	$ 1,564.6
Cash and cash equivalents		38.5	32.3	$ 37.4	$ 50.9
Income tax receivable		1.2	1.1
Deferred taxes		45.3	44.0
Property, plant and equipment, net	[1]	409.1	358.8
Operating lease right-of-use assets		102.5	112.3
Goodwill		297.8	296.1	296.5
Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets		1,543.4	1,522.0
Corporate, Non-Segment
Segment Reporting Asset Reconciling Item [Line Items]
Cash and cash equivalents		0.4	0.0
Income tax receivable		1.2	1.9
Deferred taxes		28.8	17.0
Property, plant and equipment, net		5.9	5.3
Operating lease right-of-use assets		11.9	13.2
Prepaid insurance and other assets		7.0	5.2
Railroad and Utility Products and Services [Member] | Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets		583.1	562.2
Goodwill		121.1	120.7
Carbon Materials and Chemicals [Member] | Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets		424.2	502.1
Performance Chemicals [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Goodwill		176.7	175.4	$ 175.4
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets		536.1	457.7
Goodwill		$ 176.7	$ 175.4

[1] Net property, plant, and equipment excludes $56.6 million of assets of discontinued operations held for sale related to our KJCC business as of December 31, 2019.