SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended								12 Months Ended
	Oct. 01, 2013	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	Sep. 30, 2013
FOREIGN CURRENCIES
Foreign currency gains (losses)										$ (9,300)	$ 1,600	$ (400)
Impact change in accounting principle
Cumulative effect of an accounting change to retained earnings net of income tax	$ 2,300
Net 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
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, excluding depreciation										898,805	1,703,476	2,006,715
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
Diluted earnings per common share (in dollars per share)		$ (0.68)	$ (0.20)	$ 0.19	$ 0.15	$ (0.26)	$ 0.83	$ 1.41	$ 1.86	$ (0.54)	$ 3.85	$ 6.44
Total assets		$ 6,832,019				$ 7,147,242				$ 6,832,019	$ 7,147,242
Total liabilities						2,251,396					2,251,396
Total shareholders' equity		$ 4,560,925				4,895,846				4,560,925	4,895,846	$ 4,891,169	$ 4,446,075
Previous Accounting Guidance
Impact change in accounting principle
Net income (loss) from continuing operations										$ (1,400)
As Reported
Impact change in accounting principle
Operating revenues											3,165,441	3,719,707
Operating costs, excluding depreciation											1,704,163	2,009,912
Net income (loss)											$ 422,225	$ 708,719
Diluted earnings per common share (in dollars per share)											$ 3.87	$ 6.46
Total assets						7,152,012					$ 7,152,012
Total liabilities						2,254,560					2,254,560
Total shareholders' equity						4,897,452					4,897,452
Adjustments
Impact change in accounting principle
Operating revenues											(3,739)	$ (3,739)
Operating costs, excluding depreciation											(687)	(3,197)
Net income (loss)											$ (1,798)	$ (2,156)
Diluted earnings per common share (in dollars per share)											$ (0.02)	$ (0.02)
Total assets						(4,770)					$ (4,770)
Total liabilities						(3,164)					(3,164)
Total shareholders' equity						$ (1,606)					$ (1,606)