Consolidated Statements of Comprehensive Income (Parenthetical) - 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]
Tax on (loss) gain on derivative instruments	$ 0	$ 12,016	$ 2,911
Tax on reclassifications of net losses (gains) on derivative instruments	(1,409)	(1,112)	(1,109)
Tax on benefit plans	(1,336)	2,267	2,469
Tax on reclassification of benefits plans actuarial losses and prior service cost	$ (678)	$ (454)	$ (367)