EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2021	Mar. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income, as reported	$ 149,809	$ 81,045	$ 73,846	$ 75,752	$ 230,854	$ 149,598
Basic earnings per share
Weighted average shares of common stock outstanding-basic (in shares)	96,248,000		95,584,000		96,181,000	93,747,000
Basic earnings per common share (usd per share)	$ 1.56		$ 0.78		$ 2.40	$ 1.60
Diluted earnings per share
Weighted average shares of common stock outstanding-basic (in shares)	96,248,000		95,584,000		96,181,000	93,747,000
Equity forward sale agreement (in shares)	0		0		0	4,000
Other (in shares)	370,000		306,000		417,000	322,000
Weighted average shares of common stock outstanding-diluted (in shares)	96,618,000		95,890,000		96,598,000	94,073,000
Diluted earnings per common share (usd per share)	$ 1.55		$ 0.77		$ 2.39	$ 1.59
Share-based Payment Arrangement
Diluted earnings per share
Anti-dilutive shares excluded from the calculation of diluted earnings per share (in shares)	24,101		30,708		65,334	0