CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 110,747	$ 64,853	$ 437,416
Other comprehensive income, net of tax:
Foreign currency translation adjustments	(2,922)	18,877	(9,333)
Unrealized gains on marketable securities, net of tax effects of $0, $0 and ($1) for fiscal years 2021, 2020 and 2019		7	104
Actuarial gains (losses), net of tax effects of ($77), $27 and $13 for fiscal years 2021, 2020 and 2019	354	(476)	(847)
Total other comprehensive (loss) income, net of tax	(2,568)	18,408	(10,076)
Comprehensive income	$ 108,179	$ 83,261	$ 427,340