EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Numerator:
Net income available to common shares	$ 32,899	$ 27,137	$ 71,448	$ 40,580
Denominator:
Weighted average common shares (Denominator for basis calculation) (in shares)	29,287,211	28,997,632	29,182,528	28,065,759
Weighted average effect of dilutive securities
Weighted average effect of dilutive securities (in shares)	437,968	481,482	483,908	541,274
Diluted weighted average common shares (Denominator for diluted calculation) (in shares)	29,725,179	29,479,114	29,666,436	28,607,033
Earnings per share:
Basic (in dollars per share)	$ 1.12	$ 0.94	$ 2.45	$ 1.45
Diluted (in dollars per share)	$ 1.11	$ 0.92	$ 2.41	$ 1.42
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding stock options excluded from calculation of diluted earnings per share (in shares)	111,000	216,000	79,000	110,000