CONSOLIDATED AND COMBINED STATEMENTS OF COMPREHENSIVE (LOSS) INCOME - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net (loss) income	$ (20,631)	$ 100,268	$ 5,881
Other comprehensive income (loss):
Foreign currency translation adjustments	15,805	(3,866)	(1,906)
Pension adjustments, net	1,178	(1,176)	562
Unrealized loss on available-for-sale securities	(1)
Total other comprehensive income (loss)	16,982	(5,042)	(1,344)
Comprehensive (loss) income	$ (3,649)	$ 95,226	$ 4,537