EARNINGS (LOSSES) PER COMMON SHARE - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2024	Mar. 31, 2023
Numerator:
Net income	$ 84,831	$ 95,173	$ 164,040	$ 97,145	$ 180,004	$ 261,185
Adjustment for basic earnings per share
Earnings allocated to unvested shareholders	(1,242)		(2,237)		(2,489)	(3,511)
Numerator for basic earnings per share	83,589		161,803		177,515	257,674
Adjustment for diluted earnings per share
Effect of reallocating undistributed earnings of unvested shareholders	2		6		3	6
Numerator for diluted earnings per share	$ 83,591		$ 161,809		$ 177,518	$ 257,680
Denominator:
Denominator for basic earnings (loss) per share - weighted-average shares (in shares)	98,774		103,968		98,960	104,615
Effect of dilutive shares from stock options, restricted stock and performance share units (in shares)	272		395		256	388
Denominator for diluted earnings (loss) per share - adjusted weighted-average shares (in shares)	99,046		104,363		99,216	105,003
Basic earnings per common share (in dollars per share)	$ 0.85		$ 1.55		$ 1.79	$ 2.46
Diluted earnings per common share (in dollars per share)	$ 0.84		$ 1.55		$ 1.79	$ 2.46