FINANCIAL INFORMATION BY INDUSTRY SEGMENT, GEOGRAPHIC AREA AND PRODUCT LINE, Revenue by Major Foreign Customers (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Revenue, Major Customer [Line Items]
Revenue	$ 156,729	$ 150,437	$ 142,978	$ 139,979	$ 136,784	$ 127,957	$ 119,184	$ 123,254	$ 590,123	$ 507,179	$ 430,449
Taiwan [Member]
Revenue, Major Customer [Line Items]
Revenue									130,500	130,849	122,671
South Korea [Member]
Revenue, Major Customer [Line Items]
Revenue									136,403	95,414	76,082
China [Member]
Revenue, Major Customer [Line Items]
Revenue									$ 97,254	$ 74,781	$ 59,239