CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net (loss) income	[1]	$ (8,402)	$ (14,274)	$ 151,419	$ 249,691
Other comprehensive income (loss), net of tax
Unrealized loss on investments in equity securities, net of tax of $0, $854, $0 and $9,071, respectively		0	(2,364)	0	(25,055)
Reclassifications of losses to net income on investments in equity securities, net of tax of $0, $0, $0 and $(858), respectively		0	0	0	11,647
Adjustment to postemployment benefit obligation, net of tax of $(118), $(104), $(333) and $(344), respectively		305	272	844	784
Other comprehensive income (loss)		305	(2,092)	844	(12,624)
Comprehensive (loss) income		$ (8,097)	$ (16,366)	$ 152,263	$ 237,067

[1] Includes income tax benefit related to the Tax Act of $844,000 and $57.7 million, for the three and nine months ended June 30, 2018, respectively.