EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net income (loss), as reported	$ 140,266	$ 114,702	$ 263,965	$ 149,631
Basic earnings per share
Weighted average shares of common stock outstanding-basic (shares)	87,595,000	86,275,000	87,295,000	86,182,000
Basic earnings per common share (usd per share)	$ 1.60	$ 1.33	$ 3.02	$ 1.74
Diluted earnings per share
Weighted average shares of common stock outstanding-basic (shares)	87,595,000	86,275,000	87,295,000	86,182,000
Incremental shares	394,000	826,000	395,000	811,000
Weighted average shares of common stock outstanding-diluted (shares)	87,989,000	87,101,000	87,690,000	86,993,000
Diluted (loss) earnings per common share (usd per share)	$ 1.59	$ 1.32	$ 3.01	$ 1.72
Anti-dilutive shares excluded from the calculation of diluted earnings per share	0	0	0	0