SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Computation of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Net Income
Basic earnings per share	$ 4,249	$ 99,505	$ 122,437	$ 39,081	$ 150,694	$ 112,992	$ 122,669	$ 46,218	$ 265,272	$ 432,573	$ 340,822
Stock options										0	0
Restricted stock and performance units									0	0	0
Diluted earnings per share									$ 265,272	$ 432,573	$ 340,822
Weighted Average Shares
Basic earnings per share (in shares)									64,789	64,581	64,240
Stock options (in shares)										61	239
Restricted stock and performance units (in shares)									50	388	595
Diluted earnings per share (in shares)									64,839	65,030	65,074
Per Share Amount
Basic earnings per share (in dollars per share)	$ 0.07	$ 1.54	$ 1.89	$ 0.60	$ 2.33	$ 1.75	$ 1.90	$ 0.72	$ 4.09	$ 6.70	$ 5.31
Stock options (in dollars per share)										0.00	(0.01)
Restricted stock and performance units (in dollars per share)									0.00	(0.05)	(0.06)
Diluted earnings per share (in dollars per share)	$ 0.07	$ 1.53	$ 1.89	$ 0.60	$ 2.32	$ 1.73	$ 1.89	$ 0.71	$ 4.09	$ 6.65	$ 5.24