CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 86,248	$ 123,699
Other comprehensive income (loss), net of tax
Unrealized loss on investments in equity securities, net of tax of $0 and $851, respectively	0	(2,290)
Reclassifications of losses to net income on investments in equity securities, net of tax of $0 and $2,178, respectively	0	(3,154)
Adjustment to postemployment benefit obligation, net of tax of $(96) and $(136), respectively	234	240
Other comprehensive income (loss)	234	(5,204)
Comprehensive income	$ 86,482	$ 118,495