SHAREHOLDER'S EQUITY - AOCI Reclassifications (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Amount Reclassified from Accumulated Other Comprehensive Income (Loss)
Loss on investment securities									$ 1		$ (25,989)
Income tax provision									477,169	$ 56,735	19,677
Net Income (Loss)	$ 2,453	$ (8,008)	$ (11,879)	$ 500,106	$ (22,532)	$ (21,799)	$ (48,818)	$ (35,063)	482,672	(128,212)	(56,828)
Net income (loss) attributable to parent, basic									478,326	(130,023)	(58,686)
Accumulated Other Comprehensive (Loss) Income | Reclassification out of AOCI
Amount Reclassified from Accumulated Other Comprehensive Income (Loss)
Net income (loss) attributable to parent, basic									5,249	3,333	(1,599)
Other-than-temporary impairment of available-for-sale securities | Reclassification out of AOCI
Amount Reclassified from Accumulated Other Comprehensive Income (Loss)
Loss on investment securities											1,509
Income tax provision											(583)
Net Income (Loss)											926
Defined Benefit Pension Plan
Amount Reclassified from Accumulated Other Comprehensive Income (Loss)
Reclassifications for the period, tax									(1,931)	(1,905)	1,443
Reclassifications for the period, net of tax									5,249	3,333	(2,525)
Amortization of net actuarial loss on defined benefit pension plan | Selling, general and administrative
Amount Reclassified from Accumulated Other Comprehensive Income (Loss)
Reclassifications for the period, before tax									$ 7,180	$ 5,238	$ (3,968)