Significant Accounting Policies - Segment Reporting Revenue Percentage (Detail) - Sales Revenue, Segment [Member] - Revenue from Rights Concentration Risk [Member]	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Reinforcement Materials [Member]
Segment Reporting Information [Line Items]
Revenue, by segment	54.00%	59.00%	57.00%
Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Revenue, by segment	33.00%	29.00%	30.00%
Purification Solutions [Member]
Segment Reporting Information [Line Items]
Revenue, by segment	11.00%	9.00%	10.00%
Specialty Fluids [Member]
Segment Reporting Information [Line Items]
Revenue, by segment	2.00%	3.00%	3.00%