Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net income	$ 148,921	$ 116,041	$ 97,373
Net gains (losses) on derivative instruments (net of tax of $(10), $0 and $12,016, respectively)	20	0	(16,942)
Reclassifications of net losses on derivative instruments (net of tax of $(1,118), $(1,409) and $(1,112), respectively)	2,367	1,988	1,568
Benefit plans, principally actuarial gains (losses) (net of tax of $(1,512), $(1,336) and $2,267, respectively)	3,203	1,883	(3,197)
Reclassifications of benefit plans actuarial losses and net prior service benefits (net of tax of $(411), $(678) and $(454), respectively)	872	956	639
Other comprehensive income (loss)	6,462	4,827	(17,932)
Comprehensive income	$ 155,383	$ 120,868	$ 79,441