STOCKHOLDERS' EQUITY - Stock Purchase Obligation (Details)	12 Months Ended
	Sep. 30, 2017 shares / contract $ / shares	Jun. 30, 2014 $ / shares
Stock Purchase Obligation [Line Items]
Stated value per Corporate Unit (in dollars per share)		$ 50,000,000
Equal to or greater than $57.8125
Stock Purchase Obligation [Line Items]
Market value per share of common stock (in dollars per share)	$ 57.8125
Number of shares to be purchased per purchase contract | shares / contract	0.8649
Less than $57.8125, but greater than $46.25 | Minimum
Stock Purchase Obligation [Line Items]
Market value per share of common stock (in dollars per share)	$ 46.25
Less than $57.8125, but greater than $46.25 | Maximum
Stock Purchase Obligation [Line Items]
Market value per share of common stock (in dollars per share)	57.8125
Less than or equal to $46.25
Stock Purchase Obligation [Line Items]
Market value per share of common stock (in dollars per share)	$ 46.25
Number of shares to be purchased per purchase contract | shares / contract	1.0811