EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator [Abstract]
Net income (loss)	$ 35,171	$ 19,939	$ 61,825	$ 60,450
Less: income attributable to participating securities	(34)	(52)	(73)	(191)
Earnings available to common shares	$ 35,137	$ 19,887	$ 61,752	$ 60,259
Denominator [Abstract]
Weighted average common shares (Denominator for basic calculation) (in shares)	25,611,505	25,228,468	25,479,078	24,941,190
Weighted average effect of dilutive securities [Abstract]
Share-based compensation (in shares)	707,133	492,247	742,786	508,317
Diluted weighted average common shares (Denominator for diluted calculation) (in shares)	26,318,638	25,720,715	26,221,864	25,449,507
Earnings per share [Abstract]
Basic (in dollars per share)	$ 1.37	$ 0.79	$ 2.42	$ 2.42
Diluted (in dollars per share)	$ 1.34	$ 0.77	$ 2.35	$ 2.37
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Abstract]
Outstanding stock options excluded from diluted earnings (in shares)	100,000	100,000	100,000	400,000