Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net income	$ 116,041	$ 97,373	$ 121,055
Net losses on derivative instruments (net of tax of $0, $12,016 and $2,911, respectively)	0	(16,942)	(4,105)
Reclassifications of net losses on derivative instruments (net of tax of $(1,409), $(1,112) and $(1,109), respectively)	1,988	1,568	1,565
Benefit plans, principally actuarial gains (losses) (net of tax of $(1,336), $2,267 and $2,469, respectively)	1,883	(3,197)	(3,482)
Reclassifications of benefit plans actuarial losses and net prior service credits (net of tax of $(678), $(454) and $(367), respectively)	956	639	517
Other comprehensive income (loss)	4,827	(17,932)	(5,505)
Comprehensive income	$ 120,868	$ 79,441	$ 115,550