Segment Information - Summary of Results of Segment Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenue from External Customer [Line Items]
Intersegment revenues	$ 426.7	$ 440.1	$ 356.8	$ 331.4	$ 341.8	$ 395.2	$ 370.9	$ 370.4	$ 1,555.0	$ 1,478.3	$ 1,555.0
Revenues from external customers:
Revenues from external customers	426.7	440.1	356.8	331.4	341.8	395.2	370.9	370.4	1,555.0	1,478.3	1,555.0
Intersegment revenues:
Intersegment revenues	426.7	440.1	356.8	331.4	341.8	395.2	370.9	370.4	1,555.0	1,478.3	1,555.0
Depreciation and amortization:
Depreciation and amortization expense									44.0	29.7	27.6
Operating profit:
Operating profit (loss)	2.1	17.3	13.3	0.5	7.8	39.1	28.5	24.9	33.2	100.3	126.6
Capital expenditures (including acquisitions):
Capital expenditures (including acquisitions)									580.0	75.2	42.9
Carbon Materials and Chemicals [Member]
Revenue from External Customer [Line Items]
Intersegment revenues									833.7	906.1	999.7
Revenues from external customers:
Revenues from external customers									833.7	906.1	999.7
Intersegment revenues:
Intersegment revenues									833.7	906.1	999.7
Railroad and Utility Products and Services [Member]
Revenue from External Customer [Line Items]
Intersegment revenues									597.8	572.2	555.3
Revenues from external customers:
Revenues from external customers									597.8	572.2	555.3
Intersegment revenues:
Intersegment revenues									597.8	572.2	555.3
Performance Chemicals [Member]
Revenue from External Customer [Line Items]
Intersegment revenues									123.5	0	0
Revenues from external customers:
Revenues from external customers									123.5	0	0
Intersegment revenues:
Intersegment revenues									123.5	0	0
Operating Segments [Member] | Carbon Materials and Chemicals [Member]
Revenue from External Customer [Line Items]
Intersegment revenues									833.7	906.1	999.7
Revenues from external customers:
Revenues from external customers									833.7	906.1	999.7
Intersegment revenues:
Intersegment revenues									833.7	906.1	999.7
Depreciation and amortization:
Depreciation and amortization expense									25.0	18.2	16.9
Operating profit:
Operating profit (loss)									(5.3)	43.9	83.1
Capital expenditures (including acquisitions):
Capital expenditures (including acquisitions)									63.7	58.0	17.3
Operating Segments [Member] | Railroad and Utility Products and Services [Member]
Revenue from External Customer [Line Items]
Intersegment revenues									597.8	572.2	555.3
Revenues from external customers:
Revenues from external customers									597.8	572.2	555.3
Intersegment revenues:
Intersegment revenues									597.8	572.2	555.3
Depreciation and amortization:
Depreciation and amortization expense									11.9	11.5	10.7
Operating profit:
Operating profit (loss)									53.6	58.3	45.1
Capital expenditures (including acquisitions):
Capital expenditures (including acquisitions)									44.5	15.9	25.0
Operating Segments [Member] | Performance Chemicals [Member]
Revenue from External Customer [Line Items]
Intersegment revenues									123.5	0	0
Revenues from external customers:
Revenues from external customers									123.5	0	0
Intersegment revenues:
Intersegment revenues									123.5	0	0
Depreciation and amortization:
Depreciation and amortization expense									7.1	0	0
Operating profit:
Operating profit (loss)									1.6	0	0
Capital expenditures (including acquisitions):
Capital expenditures (including acquisitions)									471.1	0	0
Intersegment [Member]
Revenue from External Customer [Line Items]
Intersegment revenues									87.8	94.2	106.5
Revenues from external customers:
Revenues from external customers									87.8	94.2	106.5
Intersegment revenues:
Intersegment revenues									87.8	94.2	106.5
Intersegment [Member] | Carbon Materials and Chemicals [Member]
Revenue from External Customer [Line Items]
Intersegment revenues									84.8	94.2	106.5
Revenues from external customers:
Revenues from external customers									84.8	94.2	106.5
Intersegment revenues:
Intersegment revenues									84.8	94.2	106.5
Intersegment [Member] | Performance Chemicals [Member]
Revenue from External Customer [Line Items]
Intersegment revenues									3.0	0	0
Revenues from external customers:
Revenues from external customers									3.0	0	0
Intersegment revenues:
Intersegment revenues									3.0	0	0
Corporate, Non-Segment [Member]
Operating profit:
Operating profit (loss)									(16.7)	(1.9)	(1.6)
Capital expenditures (including acquisitions):
Capital expenditures (including acquisitions)									$ 0.7	$ 1.3	$ 0.6