EARNINGS (LOSS) PER COMMON SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Numerator:
Income from continuing operations	$ 71,857		$ (1,633)		$ 80,221	$ 499,009
Income (loss) from discontinued operations	(10,966)		(10,246)		(371)	(10,782)
Net income (loss)	60,891	$ 18,959	(11,879)	$ 500,106	79,850	488,227
Adjustment for basic earnings per share:
Earnings allocated to unvested shareholders	(784)		(717)		(1,560)	(4,106)
Numerator for basic earnings per share:
From continuing operations	71,073		(2,350)		78,661	494,903
From discontinued operations	(10,966)		(10,246)		(371)	(10,782)
Net income (loss) attributable to parent, basic	60,107		(12,596)		78,290	484,121
Adjustment for diluted earnings per share:
Effect of reallocating undistributed earnings of unvested shareholders						11
Numerator for diluted earnings per share:
From continuing operations	71,073		(2,350)		78,661	494,914
From discontinued operations	(10,966)		(10,246)		(371)	(10,782)
Net income (loss) attributable to parent, diluted	$ 60,107		$ (12,596)		$ 78,290	$ 484,132
Denominator:
Denominator for basic earnings per share – weighted-average shares	109,406		108,868		109,273	108,775
Effect of dilutive shares from stock options, restricted stock and performance units (in shares)	97				179	437
Denominator for diluted earnings per share – adjusted weighted-average shares	109,503		108,868		109,452	109,212
Basic earnings (loss) per common share:
Income (loss) from continuing operations (in dollars per share)	$ 0.65		$ (0.03)		$ 0.72	$ 4.55
Income from discontinued operations (in dollars per share)	(0.10)		(0.09)			(0.10)
Net income (loss) (in dollars per share)	0.55		(0.12)		0.72	4.45
Diluted earnings (loss) per common share:
Income (loss) from continuing operations (in dollars per share)	0.65		(0.03)		0.72	4.53
Income from discontinued operations (in dollars per share)	(0.10)		(0.09)			(0.10)
Net income (loss) (in dollars per share)	$ 0.55		$ (0.12)		$ 0.72	$ 4.43
Outstanding equity awards
Shares excluded from calculation of diluted earnings per share (in shares)	2,921		1,613		2,770	1,676
Weighted-average price per share (in dollars per share)	$ 64.04		$ 68.69		$ 64.18	$ 68.12