Consolidated Statements Of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 130,695	$ (27,460)	$ 51,987
Other comprehensive income (loss), net of tax:
Hedge gain (loss) arising during the period, net of tax of $1.7 million, $1.7 million, and $0.2 million in 2020, 2019, and 2018, respectively	(13,242)	5,251	1,445
Net hedge gain (loss) reclassified into earnings, net of tax of $0 million, $0.1 million, and $0.1 million in 2020, 2019, and 2018, respectively	0	(549)	483
Realized and unrealized gain (loss) on hedging instruments	(13,242)	4,702	1,928
Foreign currency translation adjustment, net of tax of $0 for all periods	22,076	(24,755)	(11,767)
Unrealized gain on marketable securities, net of tax of $0 for all periods	188	530	(269)
Amortization of net actuarial pension gain included in net income, net of tax of $0.9 million, $0.7 million, and $0.7 million in 2020, 2019, and 2018, respectively	2,983	1,691	1,629
Pension net loss arising during the period net of tax of $0.7 million, $3.6 million, and $1.5 million in 2020, 2019, and 2018, respectively	(2,791)	(8,743)	(3,787)
Change in unamortized pension gain (loss) during the period related to changes in foreign currency	(1,878)	1,450	588
Other comprehensive income (loss)	7,336	(25,125)	(11,678)
Comprehensive income (loss)	$ 138,031	$ (52,585)	$ 40,309