CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 64,853	$ 437,416	$ 116,464
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	18,877	(9,333)	(1,651)
Unrealized (losses) gains on marketable securities, net of tax effects of $0, ($1) and $0 for fiscal years 2020, 2019 and 2018	7	104	(111)
Actuarial gains (losses), net of tax effects of $27, $13 and ($49) for fiscal years 2020, 2019 and 2018	(476)	(847)	136
Total other comprehensive income, net of tax	18,408	(10,076)	(1,626)
Comprehensive income	83,261	427,340	114,838
Comprehensive loss attributable to noncontrolling interest			111
Comprehensive income attributable to common stockholders	$ 83,261	$ 427,340	$ 114,949