Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 10,697	$ 12,603	$ 120,087	$ 99,248
Other comprehensive income (loss):
Net losses on derivative instruments (net of tax of $0, $0, $0, and $12,016, respectively)	0	0	0	(16,943)
Reclassifications of net losses on derivative instruments (net of tax of $(355), $(253), $(1,047), and $(782), respectively)	501	357	1,477	1,103
Benefit plans reclassifications of actuarial losses and prior service costs (net of tax of $(169), $(113), $(507), and $(340), respectively)	239	160	717	480
Other comprehensive income (loss)	740	517	2,194	(15,360)
Comprehensive income	$ 11,437	$ 13,120	$ 122,281	$ 83,888