UNAUDITED CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
UNAUDITED CONSOLIDATED STATEMENTS OF INCOME [Abstract]
Revenue	$ 139,979	$ 123,254
Cost of goods sold	65,965	61,749
Gross profit	74,014	61,505
Operating expenses:
Research, development and technical	12,151	13,396
Selling and marketing	5,836	7,552
General and administrative	18,915	12,496
Total operating expenses	36,902	33,444
Operating income	37,112	28,061
Interest expense	1,132	1,150
Other income, net	672	996
Income before income taxes	36,652	27,907
Provision for income taxes	39,735	5,676
Net income (loss)	$ (3,083)	$ 22,231
Basic earnings (loss) per share (in dollars per share)	$ (0.12)	$ 0.90
Weighted average basic shares outstanding (in shares)	25,325,757	24,582,688
Diluted earnings (loss) per share (in dollars per share)	$ (0.12)	$ 0.88
Weighted average diluted shares outstanding (in shares)	25,325,757	25,072,165
Dividends per share (in dollars per share)	$ 0.20	$ 0.18