SHAREHOLDER'S EQUITY - AOCI Reclassifications (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2019	Mar. 31, 2018
Amount Reclassified from Accumulated Other Comprehensive Income (Loss)
Other income (expense)	$ 1,789		$ (4,391)		$ (42,785)	$ (7,999)
Income tax provision	(25,078)		3,922		(26,429)	504,563
Net income (loss)	60,891	$ 18,959	(11,879)	$ 500,106	79,850	488,227
Defined Benefit Pension Plan | Amount Reclassified from Accumulated Other Comprehensive Income (Loss)
Amount Reclassified from Accumulated Other Comprehensive Income (Loss)
Income tax provision	67		152		134	273
Net income (loss)	(224)		(308)		(449)	(648)
Amortization of net actuarial loss on defined benefit pension plan | Amount Reclassified from Accumulated Other Comprehensive Income (Loss)
Amount Reclassified from Accumulated Other Comprehensive Income (Loss)
Other income (expense)	$ (291)		$ (460)		$ (583)	$ (921)