STOCK-BASED COMPENSATION - Restricted Stock (Details) - Restricted stock - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Common-stock based award plan
Unrecognized compensation cost (in dollars)	$ 21.4
Weighted-average period over which unrecognized compensation cost is expected to be recognized	2 years 2 months 12 days
Restricted stock awards activity, shares
Unvested at the beginning of the period (in shares)	648,000	668,000	634,000
Granted (in shares)	292,112	294,000	275,000
Vested (in shares)	(271,000)	(256,000)	(214,000)
Forfeited (in shares)	(10,000)	(58,000)	(27,000)
Unvested at the end of the period (in shares)	659,000	648,000	668,000
Restricted stock awards activity, weighted average grant date fair value
Unvested at the beginning of the period (in dollars per share)	$ 64.24	$ 67.03	$ 64.03
Granted (in dollars per share)	78.69	58.25	68.83
Vested (in dollars per share)	63.81	64.75	60.80
Forfeited (in dollars per share)	68.09	63.65	64.45
Unvested at the end of the period (in dollars per share)	$ 70.76	$ 64.24	$ 67.03
Minimum
Common-stock based award plan
Vesting period	3 years
Maximum
Common-stock based award plan
Vesting period	6 years