Significant Accounting Policies - Segment Reporting Revenue Percentage (Detail) - Sales Revenue, Segment [Member] - Revenue from Rights Concentration Risk [Member]	3 Months Ended		6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Reinforcement Materials [Member]
Segment Reporting Information [Line Items]
Revenue, by segment	54.00%	48.00%	52.00%	49.00%
Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Revenue, by segment	35.00%	39.00%	35.00%	38.00%
Purification Solutions [Member]
Segment Reporting Information [Line Items]
Revenue, by segment	10.00%	12.00%	11.00%	12.00%
Specialty Fluids [Member]
Segment Reporting Information [Line Items]
Revenue, by segment	1.00%	1.00%	2.00%	1.00%