Consolidated Statements of Comprehensive (Loss) Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (3,606)	$ (22,064)	$ (12,433)	$ (2,740)
Net derivative (losses) gains arising during the period, net of tax of $303, $(1,158), $1,439 and $(2,322), respectively	(756)	3,055	(3,778)	4,815
Reclassification of losses into net loss, net of tax of $710, $607, $1,013 and $1,642, respectively	1,888	1,616	2,420	3,181
Other comprehensive income (loss)	1,132	4,671	(1,358)	7,996
Comprehensive (loss) income	$ (2,474)	$ (17,393)	$ (13,791)	$ 5,256