GUARANTOR AND NON-GUARANTOR FINANCIAL INFORMATION - Statement of Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
CONDENSED CONSOLIDATING STATEMENTS OF OPERATIONS
Operating revenues	$ 331,708	$ 366,486	$ 438,191	$ 487,847	$ 553,800	$ 661,445	$ 885,670	$ 1,060,787	$ 1,624,232	$ 3,161,702	$ 3,715,968
Operating costs and other									1,650,198	2,489,739	2,662,794
Operating income (loss) from continuing operations	(93,001)	(13,256)	41,621	38,670	(24,783)	135,049	231,326	330,371	(25,966)	671,963	1,053,174
Other income, net										4,939	46,141
Other expense, net									(23,788)
Interest expense									(22,913)	(15,023)	(4,657)
Income (loss) from continuing operations before income taxes									(72,667)	661,879	1,094,658
Income tax provision (benefit)									(19,677)	241,405	388,048
Income (loss) from continuing operations	(72,869)	(21,193)	25,174	15,898	(27,590)	90,899	153,542	203,623	(52,990)	420,474	706,610
Income (loss) from discontinued operations before income taxes									2,360	(124)	2,758
Income tax provision (benefit)									6,198	(77)	2,805
Loss from discontinued operations									(3,838)	(47)	(47)
NET INCOME (LOSS)	$ (72,835)	$ (21,200)	$ 21,205	$ 16,002	$ (27,596)	$ 90,872	$ 153,543	$ 203,608	(56,828)	420,427	706,563
Eliminations
CONDENSED CONSOLIDATING STATEMENTS OF OPERATIONS
Operating revenues									(70)	(75)	(152)
Operating costs and other									(1,323)	(3,104)	(4,300)
Operating income (loss) from continuing operations									1,253	3,029	4,148
Other income, net											(4,148)
Other expense, net									(1,253)	(3,029)
Equity in net income (loss) of subsidiaries									61,638	(414,214)	(715,525)
Income (loss) from continuing operations before income taxes									61,638	(414,214)	(715,525)
Income (loss) from continuing operations									61,638	(414,214)	(715,525)
NET INCOME (LOSS)									61,638	(414,214)	(715,525)
Guarantor/Parent | Reportable Legal Entities
CONDENSED CONSOLIDATING STATEMENTS OF OPERATIONS
Operating costs and other									13,145	10,875	10,763
Operating income (loss) from continuing operations									(13,145)	(10,875)	(10,763)
Other income, net											57
Other expense, net									(194)	(91)
Interest expense									(375)	(159)	(42)
Equity in net income (loss) of subsidiaries									(47,166)	427,342	713,001
Income (loss) from continuing operations before income taxes									(60,880)	416,217	702,253
Income tax provision (benefit)									(4,052)	(4,210)	(4,310)
Income (loss) from continuing operations									(56,828)	420,427	706,563
NET INCOME (LOSS)									(56,828)	420,427	706,563
Issuer Subsidiary | Reportable Legal Entities
CONDENSED CONSOLIDATING STATEMENTS OF OPERATIONS
Operating revenues									1,373,511	2,735,863	3,325,039
Operating costs and other									1,358,269	2,037,465	2,291,775
Operating income (loss) from continuing operations									15,242	698,398	1,033,264
Other income, net										7,523	48,108
Other expense, net									(22,243)
Interest expense									(20,256)	(8,955)	(3,049)
Equity in net income (loss) of subsidiaries									(14,472)	(13,128)	2,524
Income (loss) from continuing operations before income taxes									(41,729)	683,838	1,080,847
Income tax provision (benefit)									5,127	258,536	370,734
Income (loss) from continuing operations									(46,856)	425,302	710,113
NET INCOME (LOSS)									(46,856)	425,302	710,113
Non-Guarantor Subsidiaries | Reportable Legal Entities
CONDENSED CONSOLIDATING STATEMENTS OF OPERATIONS
Operating revenues									250,791	425,914	391,081
Operating costs and other									280,107	444,503	364,556
Operating income (loss) from continuing operations									(29,316)	(18,589)	26,525
Other income, net										536	2,124
Other expense, net									(98)
Interest expense									(2,282)	(5,909)	(1,566)
Income (loss) from continuing operations before income taxes									(31,696)	(23,962)	27,083
Income tax provision (benefit)									(20,752)	(12,921)	21,624
Income (loss) from continuing operations									(10,944)	(11,041)	5,459
Income (loss) from discontinued operations before income taxes									2,360	(124)	2,758
Income tax provision (benefit)									6,198	(77)	2,805
Loss from discontinued operations									(3,838)	(47)	(47)
NET INCOME (LOSS)									$ (14,782)	$ (11,088)	$ 5,412