Consolidated Statements of Comprehensive (Loss) Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net (loss) income	$ (8,827)	$ 19,324
Net derivative (losses) gains arising during the period, net of tax of $(1,135) and $1,164, respectively	(3,022)	1,760
Reclassification of gains into net (loss) income, net of tax of $304 and $1,035, respectively	532	1,565
Other comprehensive (loss) income	(2,490)	3,325
Comprehensive (loss) income	$ (11,317)	$ 22,649