CONSOLIDATED STATEMENTS OF INCOME - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Revenue	$ 1,116,270,000	$ 1,037,696,000	$ 590,123,000
Cost of sales	627,669,000	595,043,000	276,018,000
Gross profit	488,601,000	442,653,000	314,105,000
Operating expenses:
Research, development and technical	52,311,000	51,707,000	51,950,000
Selling, general and administrative	217,071,000	213,078,000	102,037,000
Asset impairment charges	2,314,000	67,372,000	0
Total operating expenses	271,696,000	332,157,000	153,987,000
Operating income (loss)	216,905,000	110,496,000	160,118,000
Interest expense	42,510,000	45,681,000	2,905,000
Interest income	670,000	2,346,000	4,409,000
Other income (expense), net	(1,718,000)	(4,055,000)	89,000
Income before income taxes	173,347,000	63,106,000	161,711,000
Provision for income taxes	30,519,000	23,891,000	51,668,000
Net income	$ 142,828,000	$ 39,215,000	$ 110,043,000
Basic earnings per share (in dollars per share)	$ 4.90	$ 1.37	$ 4.31
Weighted average basic shares outstanding (in shares)	29,136,000	28,571,000	25,518,000
Diluted earnings per share (in dollars per share)	$ 4.83	$ 1.35	$ 4.19
Weighted average diluted shares outstanding (in shares)	29,580,000	29,094,000	26,243,000