Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ (10,612)	$ 98,626	$ 100,864
Other comprehensive income (loss):
Foreign currency translation adjustment	(1,734)	(2,687)	3,706
Unrealized gain (loss) due to change in fair value of derivatives, net of tax	(1,612)	0	0
Total other comprehensive income (loss)	(3,346)	(2,687)	3,706
Comprehensive income (loss)	$ (13,958)	$ 95,939	$ 104,570