CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ (14,274)	$ 18,957	$ 249,691	$ 168,588
Other comprehensive (loss) income, net of tax
Unrealized (loss) gain on available for sale securities, net of tax of $854, $2,375, $9,071 and $(2,801), respectively	(2,364)	(3,622)	(25,055)	3,301
Reclassifications of losses to net income on available for sale securities, net of tax of $0, $0, $(858) and $0, respectively	0	0	11,647	0
Adjustment to postemployment benefit obligation, net of tax of $(104), $(217), $(344) and $(651), respectively	272	318	784	953
Other comprehensive (loss) income	(2,092)	(3,304)	(12,624)	4,254
Comprehensive (loss) income	$ (16,366)	$ 15,653	$ 237,067	$ 172,842