Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ (3,023)	$ 10,697	$ 154,464	$ 120,087
Other comprehensive income:
Reclassifications of net losses on derivative instruments (net of tax of $(279), $(355), $(838) and $(1,047), respectively)	592	501	1,776	1,477
Benefit plans reclassifications of actuarial losses and net prior service credits (net of tax of $(104), $(169), $(312) and $(507), respectively)	220	239	660	717
Other comprehensive income	812	740	2,436	2,194
Comprehensive (loss) income	$ (2,211)	$ 11,437	$ 156,900	$ 122,281