EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator [Abstract]
Net income	$ 19,939	$ 18,702	$ 60,450	$ 39,142
Less: income attributable to participating securities	(52)	(110)	(191)	(260)
Earnings available to common shares	$ 19,887	$ 18,592	$ 60,259	$ 38,882
Denominator [Abstract]
Weighted average common shares (Denominator for basic calculation) (in shares)	25,228,468	23,928,512	24,941,190	24,022,809
Weighted average effect of dilutive securities [Abstract]
Share-based compensation (in shares)	492,247	396,654	508,317	380,071
Diluted weighted average common shares (Denominator for diluted calculation) (in shares)	25,720,715	24,325,166	25,449,507	24,402,880
Earnings per share [Abstract]
Basic (in dollars per share)	$ 0.79	$ 0.78	$ 2.42	$ 1.62
Diluted (in dollars per share)	$ 0.77	$ 0.76	$ 2.37	$ 1.59
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding stock options excluded from diluted earnings (in shares)	100,000	1,200,000	400,000	1,200,000