EQUITY-BASED INCENTIVE AWARDS - Stock Options (Details) $ / shares in Units, $ in Millions	3 Months Ended
	Dec. 31, 2017 USD ($) item $ / shares shares	Dec. 31, 2016 USD ($) shares	Sep. 30, 2017 $ / shares shares
Omnibus plan and stock option activity
Number of incentive plans | item	2
Number of shares of the company's common stock permitted for issuance under the plan	225,000
Number of shares awarded pursuant to the plan	208,815
Number of additional shares that may be awarded under the plan	16,185
Aggregate intrinsic value and fair value of options outstanding
Compensation expense related to the amortization of all equity - based compensation awards | $	$ 0.3	$ 0.5
Stock Options
Omnibus plan and stock option activity
Expiration period	10 years	10 years
Vesting period	5 years	5 years
Estimated fair value of the stock option awards using the Black-Scholes option pricing model | $	$ 0.2	$ 0.1
Stock Option Pricing Assumptions
Risk-free interest rate (as a percent)	2.41%	2.12%
Dividend yield (as a percent)	0.80%	0.60%
Expected volatility (as a percent)	33.00%	22.40%
Expected life	6 years	6 years
Stock options issued and outstanding
Number Outstanding (in shares)	34,300		28,300
Weighted-Average Exercise Price (in dollars per share) | $ / shares	$ 77.50		$ 74.75
Number of Shares
Granted (in shares)	6,000	6,000
Weighted Average Exercise Price
Granted (in dollars per share) | $ / shares	$ 90.50