CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 437,416	$ 116,464	$ 62,612
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	(9,333)	(1,651)	(221)
Unrealized gains (losses) on marketable securities, net of tax effects of ($1), $0 and $0 for fiscal years 2019, 2018 and 2017	104	(111)	2
Actuarial gains (loss), net of tax effects of $13, ($49) and ($74) for fiscal years 2019, 2018 and 2017	(847)	136	525
Pension settlement			(259)
Total other comprehensive (loss) income, net of tax	(10,076)	(1,626)	47
Comprehensive income	427,340	114,838	62,659
Comprehensive loss attributable to noncontrolling interest		111
Comprehensive income attributable to common stockholders	$ 427,340	$ 114,949	$ 62,659