Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 63,294	$ 79,589	$ 86,645	$ 118,428
Other comprehensive income (loss):
Net losses on derivative instruments (net of tax of $13,348, $0, $12,016 and $0, respectively)	(18,820)	0	(16,943)	0
Reclassifications of net losses on derivative instruments (net of tax of $(253), $(278), $(529) and $(556), respectively)	356	392	746	783
Benefit plans reclassifications of actuarial losses and prior service costs (net of tax of $(114), $(92), $(227) and $(183), respectively)	160	129	320	260
Other comprehensive (loss) income	(18,304)	521	(15,877)	1,043
Comprehensive income	$ 44,990	$ 80,110	$ 70,768	$ 119,471