Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net income	$ 97,373	$ 121,055	$ 124,106
Net losses on derivative instruments (net of tax of $12,016, $2,911 and $0, respectively)	(16,942)	(4,105)	0
Reclassifications of net losses on derivative instruments (net of tax of $(1,112), $(1,109) and $(1,112), respectively)	1,568	1,565	1,567
Benefit plans, principally actuarial losses (net of tax of $2,267, $2,469 and $1,002, respectively)	(3,197)	(3,482)	(1,413)
Reclassifications of benefit plans actuarial losses and net prior service credits (net of tax of $(454), $(367) and $(274), respectively)	639	517	385
Other comprehensive (loss) income	(17,932)	(5,505)	539
Comprehensive income	$ 79,441	$ 115,550	$ 124,645