SHAREHOLDERS’ EQUITY - AOCI Reclassifications (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Accumulated other comprehensive income (loss) components which were reclassified to the Consolidated Statement of Operations
Loss on investment securities										$ (25,989)
Income tax provision									$ 56,735	19,677	$ (241,405)
Net income (loss)	$ (22,532)	$ (21,799)	$ (48,818)	$ (35,063)	$ (72,835)	$ (21,200)	$ 21,205	$ 16,002	(128,212)	(56,828)	$ 420,427
Accumulated Other Comprehensive Loss
Accumulated other comprehensive income (loss) components which were reclassified to the Consolidated Statement of Operations
Total reclassifications for the period									3,333	(1,599)
Other-than-temporary impairment of available-for-sale securities | Reclassification out of AOCI
Accumulated other comprehensive income (loss) components which were reclassified to the Consolidated Statement of Operations
Loss on investment securities										1,509
Income tax provision										(583)
Net income (loss)										926
Defined benefit pension plan
Accumulated other comprehensive income (loss) components which were reclassified to the Consolidated Statement of Operations
Reclassifications for the period, tax									(1,905)	1,443
Total reclassifications for the period									3,333	(2,525)
Amortization of net actuarial loss on defined benefit pension plan | General and Administrative
Accumulated other comprehensive income (loss) components which were reclassified to the Consolidated Statement of Operations
Reclassifications for the period, before tax									$ 5,238	$ (3,968)