Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 49,888	$ 68,303
Other comprehensive income (loss):
Net losses on derivative instruments (net of tax of $487 and $0, respectively)	(1,198)	0
Reclassifications of net losses on derivative instruments (net of tax of $(252) and $(279), respectively)	620	592
Reclassifications of benefit plans actuarial losses and net prior service benefits (net of tax of $(54) and $(104), respectively)	132	220
Other comprehensive (loss) income	(446)	812
Comprehensive income	$ 49,442	$ 69,115