Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net income	$ 121,055	$ 124,106	$ 102,098
Net (losses) gains on derivative instruments (net of tax of $2,911, $0 and $(10,746), respectively)	(4,105)	0	15,153
Reclassifications of net losses on derivative instruments	1,565	1,567	471
Benefit plans (net of tax of $2,469, $1,002 and $(3,325), respectively)	(3,482)	(1,413)	4,689
Reclassifications of benefit plans actuarial losses and prior service costs (net of tax of $(367), $(274) and $(555), respectively)	517	385	784
Other comprehensive (loss) income	(5,505)	539	21,097
Comprehensive income	$ 115,550	$ 124,645	$ 123,195