EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017		Sep. 30, 2016		Sep. 30, 2015
Earnings Per Share [Abstract]
Net income, as reported	$ (36,523)	$ 18,957	$ 114,702	$ 34,929	$ 25,400	$ (17,363)	$ 73,354	$ 50,281	$ 132,065		$ 131,672		$ 180,960
Basic earnings per share
Weighted average shares of common stock outstanding-basic (in shares)									86,321,000		85,884,000		85,186,000
Basic earnings per common share (in dollars per share)	$ (0.42)	$ 0.22	$ 1.33	$ 0.41	$ 0.30	$ (0.20)	$ 0.85	$ 0.59	$ 1.53		$ 1.53		$ 2.12
Diluted earnings per share
Weighted average shares of common stock outstanding-basic (in shares)									86,321,000		85,884,000		85,186,000
Incremental shares (in shares)									823,000		847,000		1,079,000
Weighted average shares of common stock outstanding-diluted (in shares)									87,144,000		86,731,000		86,265,000
Diluted earnings per common share (in dollars per share)	$ (0.42)	$ 0.22	$ 1.32	$ 0.40	$ 0.29	$ (0.20)	$ 0.84	$ 0.58	$ 1.52	[1]	$ 1.52	[1]	$ 2.10	[1]
Anti-dilutive securities excluded from the calculation of diluted earnings per share (in shares)									0		0		0

[1] There were no anti-dilutive shares excluded from the calculation of diluted earnings per share for fiscal 2017, 2016 and 2015.