Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 12,603	$ 7,307	$ 99,248	$ 125,735
Other comprehensive (loss) income:
Net losses on derivative instruments (net of tax of $0, $0, $12,016 and $0, respectively)	0	0	(16,943)	0
Reclassifications of net losses on derivative instruments (net of tax of $(253), $(277), $(782) and $(833), respectively)	357	392	1,103	1,175
Benefit plans reclassifications of actuarial losses and prior service costs (net of tax of $(113), $(92), $(340) and $(275), respectively)	160	128	480	388
Other comprehensive income (loss)	517	520	(15,360)	1,563
Comprehensive income	$ 13,120	$ 7,827	$ 83,888	$ 127,298