CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 88,505	$ 73,573	$ 177,866	$ 159,821
Other comprehensive (loss) income, net of tax
Unrealized loss on derivatives designated as hedging instruments, net of tax of $2,781	(9,711)	0	(9,711)	0
Adjustment to postemployment benefit obligation, net of tax of $(1,753), $(119), $(1,970) and $(215), respectively	6,100	305	6,859	539
Other comprehensive (loss) income	(3,611)	305	(2,852)	539
Comprehensive income	$ 84,894	$ 73,878	$ 175,014	$ 160,360