Condensed 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 Comprehensive Income [Abstract]
Net income (loss)	$ 6,673	$ (3,023)	$ 139,421	$ 154,464
Other comprehensive income (loss):
Net losses on derivative instruments (net of tax of $486, $0, $1,225 and $0, respectively)	(1,197)	0	(3,016)	0
Reclassifications of net losses on derivative instruments (net of tax of $(252), $(279), $(755) and $(838), respectively)	620	592	1,859	1,776
Reclassifications of benefit plan actuarial losses and net prior service benefits (net of tax of $(53), $(104), $(161) and $(312), respectively)	132	220	397	660
Other comprehensive (loss) income	(445)	812	(760)	2,436
Comprehensive income (loss)	$ 6,228	$ (2,211)	$ 138,661	$ 156,900