Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 82,860	$ 89,184	$ 132,748	$ 157,487
Other comprehensive income (loss):
Net losses on derivative instruments (net of tax of $252, $0, $739 and $0, respectively)	(621)	0	(1,819)	0
Reclassifications of net losses on derivative instruments (net of tax of $(251), $(280), $(503) and $(559), respectively)	619	592	1,239	1,184
Reclassifications of benefit plans actuarial losses and net prior service benefits (net of tax of $(54), $(104), $(108) and $(208), respectively)	133	220	265	440
Other comprehensive income (loss)	131	812	(315)	1,624
Comprehensive income	$ 82,991	$ 89,996	$ 132,433	$ 159,111