SHAREHOLDERS' EQUITY (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Changes in shareholder's equity
Beginning Balance			$ 961,595
Net earnings common stockholders	$ 16,314	$ 17,822	30,000	$ 104,599
Ending Balance	995,007	926,207	995,007	926,207
Common Stock
Changes in shareholder's equity
Beginning Balance	306	306	306	306
Ending Balance	306	306	306	306
Additional paid-in-capital
Changes in shareholder's equity
Beginning Balance	294,735	293,056	293,682	292,408
Stock plans	1,061	1,731	2,114	2,379
Ending Balance	295,796	294,787	295,796	294,787
Retained Earnings
Changes in shareholder's equity
Beginning Balance	790,000	769,439	778,398	684,741
Net earnings common stockholders	16,314	17,822	30,000	104,599
Dividends paid	(2,083)	(2,077)	(4,167)	(4,156)
Ending Balance	804,231	785,184	804,231	785,184
Accumulated other comprehensive income (loss)
Changes in shareholder's equity
Beginning Balance	1,692	(40,051)	(3,657)	(43,974)
Foreign currency translation	116	(6,885)	5,465	(2,962)
Ending Balance	1,808	(46,936)	1,808	(46,936)
Treasury Stock
Changes in shareholder's equity
Beginning Balance	(107,134)	(107,259)	(107,134)	(107,259)
Issued under stock plans		125		125
Ending Balance	$ (107,134)	$ (107,134)	$ (107,134)	$ (107,134)