Significant Accounting Policies - Segment Reporting Revenue Percentage (Detail)	3 Months Ended		6 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Reinforcement Materials [Member]
Segment Reporting Information [Line Items]
Revenue, by segment	53.00%	58.00%	56.00%	59.00%
Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Revenue, by segment	35.00%	30.00%	32.00%	29.00%
Purification Solutions [Member]
Segment Reporting Information [Line Items]
Revenue, by segment	11.00%	9.00%	10.00%	9.00%
Specialty Fluids [Member]
Segment Reporting Information [Line Items]
Revenue, by segment	1.00%	3.00%	2.00%	3.00%