EARNINGS (LOSS) PER COMMON SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Net (Loss) Income
Basic (loss) earnings per share	$ (28,862)	$ 122,437	$ (19,191)	$ 161,518
Restricted stock and performance units	0	0	0	0
Diluted (loss) earnings per share	$ (28,862)	$ 122,437	$ (19,191)	$ 161,518
Shares
Basic earnings per share (in shares)	78,270,000	64,781,000	71,504,000	64,739,000
Restricted stock and performance units (in shares)	0	44,000	0	131,000
Diluted (loss) earnings per share (in shares)	78,270,000	64,825,000	71,504,000	64,870,000
Per Share Amount
Basic earnings per share (in dollars per share)	$ (0.37)	$ 1.89	$ (0.27)	$ 2.49
Restricted stock and performance units (in dollars per share)	0.00	0.00	0.00	0.00
Diluted (loss) earnings per share (in dollars per share)	$ (0.37)	$ 1.89	$ (0.27)	$ 2.49
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding stock options, excluded in the calculation of earnings per share (in shares)	2,783,284	2,090,399	3,189,282	2,085,649
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding stock options, excluded in the calculation of earnings per share (in shares)	911,370		505,372