GUARANTOR AND NON-GUARANTOR FINANCIAL INFORMATION - Statement of Income (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
CONSOLIDATED CONDENSED STATEMENTS OF OPERATIONS
Operating revenue	$ 532,304	$ 498,564	$ 405,283	$ 368,590	$ 331,708	$ 366,486	$ 438,191	$ 487,847	$ 1,804,741	$ 1,624,232	$ 3,161,702
Operating costs and other									1,977,282	1,650,198	2,489,739
Operating income (loss) from continuing operations	(29,677)	(28,028)	(65,672)	(49,164)	(93,001)	(13,256)	41,621	38,670	(172,541)	(25,966)	671,963
Other income (expense), net									7,690	(23,788)	4,939
Interest expense									(19,747)	(22,913)	(15,023)
Income (loss) from continuing operations before income taxes									(184,598)	(72,667)	661,879
Income tax provision									(56,735)	(19,677)	241,405
Income (loss) from continuing operations	(21,711)	(23,125)	(48,473)	(34,554)	(72,869)	(21,193)	25,174	15,898	(127,863)	(52,990)	420,474
Income (loss) from discontinued operations before income taxes									3,285	2,360	(124)
Income tax provision (benefit)									3,634	6,198	(77)
Loss from discontinued operations									(349)	(3,838)	(47)
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
Eliminations
CONSOLIDATED CONDENSED STATEMENTS OF OPERATIONS
Operating revenue									(67)	(70)	(75)
Operating costs and other									(882)	(1,323)	(3,104)
Operating income (loss) from continuing operations									815	1,253	3,029
Other income (expense), net									(815)	(1,253)	(3,029)
Equity in net income (loss) of subsidiaries									124,224	61,638	(414,214)
Income (loss) from continuing operations before income taxes									124,224	61,638	(414,214)
Income (loss) from continuing operations									124,224	61,638	(414,214)
NET INCOME (LOSS)									124,224	61,638	(414,214)
Guarantor/Parent | Reportable Legal Entities
CONSOLIDATED CONDENSED STATEMENTS OF OPERATIONS
Operating costs and other									16,566	13,145	10,875
Operating income (loss) from continuing operations									(16,566)	(13,145)	(10,875)
Other income (expense), net									(240)	(194)	(91)
Interest expense									(398)	(375)	(159)
Equity in net income (loss) of subsidiaries									(116,212)	(47,166)	427,342
Income (loss) from continuing operations before income taxes									(133,416)	(60,880)	416,217
Income tax provision									(5,204)	(4,052)	(4,210)
Income (loss) from continuing operations									(128,212)	(56,828)	420,427
NET INCOME (LOSS)									(128,212)	(56,828)	420,427
Issuer Subsidiary | Reportable Legal Entities
CONSOLIDATED CONDENSED STATEMENTS OF OPERATIONS
Operating revenue									1,575,787	1,373,511	2,735,863
Operating costs and other									1,707,473	1,358,269	2,037,465
Operating income (loss) from continuing operations									(131,686)	15,242	698,398
Other income (expense), net									7,342	(22,243)	7,523
Interest expense									(20,136)	(20,256)	(8,955)
Equity in net income (loss) of subsidiaries									(8,012)	(14,472)	(13,128)
Income (loss) from continuing operations before income taxes									(152,492)	(41,729)	683,838
Income tax provision									(38,600)	5,127	258,536
Income (loss) from continuing operations									(113,892)	(46,856)	425,302
NET INCOME (LOSS)									(113,892)	(46,856)	425,302
Non-Guarantor Subsidiaries | Reportable Legal Entities
CONSOLIDATED CONDENSED STATEMENTS OF OPERATIONS
Operating revenue									229,021	250,791	425,914
Operating costs and other									254,125	280,107	444,503
Operating income (loss) from continuing operations									(25,104)	(29,316)	(18,589)
Other income (expense), net									1,403	(98)	536
Interest expense									787	(2,282)	(5,909)
Income (loss) from continuing operations before income taxes									(22,914)	(31,696)	(23,962)
Income tax provision									(12,931)	(20,752)	(12,921)
Income (loss) from continuing operations									(9,983)	(10,944)	(11,041)
Income (loss) from discontinued operations before income taxes									3,285	2,360	(124)
Income tax provision (benefit)									3,634	6,198	(77)
Loss from discontinued operations									(349)	(3,838)	(47)
NET INCOME (LOSS)									$ (10,332)	$ (14,782)	$ (11,088)