Significant Accounting Policies - Segment Reporting Revenue Percentage (Detail) - Sales Revenue, Segment [Member] - Revenue from Rights Concentration Risk [Member]	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reinforcement Materials [Member]
Segment Reporting Information [Line Items]
Revenue, by segment	57.00%	54.00%	57.00%	53.00%
Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Revenue, by segment	33.00%	34.00%	33.00%	35.00%
Purification Solutions [Member]
Segment Reporting Information [Line Items]
Revenue, by segment	9.00%	10.00%	9.00%	11.00%
Specialty Fluids [Member]
Segment Reporting Information [Line Items]
Revenue, by segment	1.00%	2.00%	1.00%	1.00%