INCOME TAXES - Effective tax rate (Details)	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Effective income tax rates as compared to the U.S. Federal income tax rate
U.S. Federal income tax rate (as a percent)	24.50%	35.00%	35.00%
Effect of foreign taxes (as a percent)	87.80%	1.80%	(13.80%)
State income taxes, net of federal tax benefit (as a percent)	68.80%	0.60%	3.20%
U.S. domestic production activities (as a percent)		(2.10%)	(10.40%)
Remeasurement of deferred tax related to Tax Reform Act (as a percent)	(3169.40%)
Other impact of foreign operations (as a percent)	(43.40%)	(2.90%)	14.70%
Non-deductible meals and entertainment (as a percent)	8.20%
Equity compensation (as a percent)	(5.30%)
Officer's compensation (as a percent)	1.70%
Contingent consideration adjustment (as a percent)	10.70%
Other (1) (as a percent)	4.10%	(1.70%)	(1.60%)
Effective income tax rate (as a percent)	(3012.30%)	30.70%	27.10%