FINANCIAL INFORMATION BY INDUSTRY SEGMENT AND PRODUCT LINE (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) Segment	Jun. 30, 2017 USD ($)
FINANCIAL INFORMATION BY INDUSTRY SEGMENT AND PRODUCT LINE [Abstract]
Number of segments | Segment			1
Revenue from External Customers by Products and Services [Abstract]
Revenue	$ 150,437	$ 127,957	$ 433,394	$ 370,395
Tungsten Slurries [Member]
Revenue from External Customers by Products and Services [Abstract]
Revenue	64,313	54,731	187,618	161,867
Dielectric Slurries [Member]
Revenue from External Customers by Products and Services [Abstract]
Revenue	36,616	30,266	102,877	87,391
Polishing Pads [Member]
Revenue from External Customers by Products and Services [Abstract]
Revenue	20,918	17,599	60,813	50,947
Other Metals Slurries [Member]
Revenue from External Customers by Products and Services [Abstract]
Revenue	18,124	16,090	51,476	46,540
ESF and Other [Member]
Revenue from External Customers by Products and Services [Abstract]
Revenue	$ 10,466	$ 9,271	$ 30,610	$ 23,650