EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share [Abstract]
Net income, as reported	$ 88,505	$ 89,361	$ 73,573	$ 86,248	$ 177,866	$ 159,821
Basic earnings per share
Weighted average shares of common stock outstanding-basic (in shares)	95,584,000		88,836,000		93,747,000	88,692,000
Basic (loss) earnings per common share (usd per share)	$ 0.93		$ 0.83		$ 1.90	$ 1.80
Diluted earnings per share
Weighted average shares of common stock outstanding-basic (in shares)	95,584,000		88,836,000		93,747,000	88,692,000
Equity forward sale agreement (in shares)	0		0		4,000	0
Other (in shares)	306,000		392,000		322,000	401,000
Weighted average shares of common stock outstanding-diluted (in shares)	95,890,000		89,228,000		94,073,000	89,093,000
Diluted (loss) earnings per common share (usd per share)	$ 0.92		$ 0.82		$ 1.89	$ 1.79
Anti-dilutive shares excluded from the calculation of diluted earnings per share (in shares)	30,708		0		0	0