EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended						6 Months Ended
		Mar. 31, 2019		Dec. 31, 2018	Mar. 31, 2018		Dec. 31, 2017	Mar. 31, 2019		Mar. 31, 2018
Earnings Per Share [Abstract]
Net income, as reported		$ 73,573	[1]	$ 86,248	$ 140,266	[1]	$ 123,699	$ 159,821	[1]	$ 263,965	[1]
Basic earnings per share
Weighted average shares of common stock outstanding-basic (shares)		88,836,000			87,595,000			88,692,000		87,295,000
Basic earnings per common share (usd per share)		$ 0.83			$ 1.60			$ 1.80		$ 3.02
Diluted earnings per share
Weighted average shares of common stock outstanding-basic (shares)		88,836,000			87,595,000			88,692,000		87,295,000
Incremental shares (shares)	[2]	392,000			394,000			401,000		395,000
Weighted average shares of common stock outstanding-diluted (shares)		89,228,000			87,989,000			89,093,000		87,690,000
Diluted earnings per common share (usd per share)	[3]	$ 0.82			$ 1.59			$ 1.79		$ 3.01
Anti-dilutive shares excluded from the calculation of diluted earnings per share		0			0			0		0

[1] Includes income tax benefit related to the Tax Act of $967,000 and $58.5 million, for the three and six months ended March 31, 2018, respectively.

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

[3] There were no anti-dilutive shares excluded from the calculation of diluted earnings per share during fiscal 2019 and 2018.