Segment Information - Summary of Tangible and Intangible Assets by Segments (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Asset Reconciling Item [Line Items]
Assets	$ 1,200,200,000	$ 1,087,500,000
Cash and cash equivalents	60,300,000	20,800,000	$ 21,800,000	$ 51,100,000
Income tax receivable	1,700,000	3,800,000
Deferred taxes	51,900,000	69,100,000
Property, plant and equipment, net	328,000,000	280,800,000
Goodwill	188,200,000	186,400,000	186,600,000
Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	1,157,900,000	1,040,100,000
Corporate, Non-Segment [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Cash and cash equivalents	700,000	0
Income tax receivable	1,700,000	3,800,000
Deferred taxes	29,400,000	32,500,000
Property, plant and equipment, net	5,200,000	4,900,000
Deferred charges	200,000	700,000
Other	5,100,000	5,500,000
Railroad and Utility Products and Services [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Goodwill	10,500,000	9,900,000	9,900,000
Railroad and Utility Products and Services [Member] | Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	249,700,000	264,200,000
Goodwill	10,500,000	9,900,000
Carbon Materials and Chemicals [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Goodwill			0
Carbon Materials and Chemicals [Member] | Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	414,200,000	333,000,000
Performance Chemicals [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Goodwill	177,700,000	176,500,000	$ 176,700,000
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	494,000,000	442,900,000
Goodwill	$ 177,700,000	$ 176,500,000