Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 31,709	$ (1,397)	$ 19,276	$ (4,139)
Net derivative (losses) gains arising during the period, net of tax of $854, $(559), $2,293 and $(2,881), respectively	(2,273)	1,488	(6,051)	6,303
Reclassification of losses into net income (loss), net of tax of $422, $688, $1,435 and $2,330, respectively	1,122	1,827	3,542	5,008
Other comprehensive (loss) income	(1,151)	3,315	(2,509)	11,311
Comprehensive income	$ 30,558	$ 1,918	$ 16,767	$ 7,172