EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended								9 Months Ended
		Jun. 30, 2019		Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018		Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2019		Jun. 30, 2018
Earnings Per Share [Abstract]
Net (loss) income, as reported		$ (8,402)	[1]	$ 73,573	$ 86,248	$ (14,274)	[1]	$ 140,266	$ 123,699	$ 151,419	[1]	$ 249,691	[1]
Basic (loss) earnings per share
Weighted average shares of common stock outstanding-basic (shares)		89,600,000				87,888,000				88,995,000		87,493,000
Basic (loss) earnings per common share (usd per share)		$ (0.09)				$ (0.16)				$ 1.70		$ 2.85
Diluted earnings per share
Weighted average shares of common stock outstanding-basic (shares)		89,600,000				87,888,000				88,995,000		87,493,000
Incremental shares (shares)	[2]	0				0				407,000		391,000
Weighted average shares of common stock outstanding-diluted (shares)		89,600,000				87,888,000				89,402,000		87,884,000
Diluted (loss) earnings per common share (usd per share)	[3]	$ (0.09)				$ (0.16)				$ 1.69		$ 2.84
Anti-dilutive shares excluded from the calculation of diluted earnings per share		409,000				402,000				0		0

[1] Includes income tax benefit related to the Tax Act of $844,000 and $57.7 million, for the three and nine months ended June 30, 2018, respectively.

[2] Incremental shares consist primarily of unvested stock awards and performance shares.

[3] Since there was a net loss for the three months ended June 30, 2019 and 2018, incremental shares of 409,000 and 402,000, respectively, were not included in the computation of diluted loss per common share, as their effect would have been anti-dilutive.There were no anti-dilutive shares excluded from the calculation of diluted earnings per share during the nine months ended June 30, 2019 and 2018.