RELINQUISHMENT AGREEMENT (Details) - USD ($)		12 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 1998
RELINQUISHMENT AGREEMENT [Abstract]
Term of relinquishment agreement		15 years
Relinquishment liability		$ 0	$ 0		$ 549,100,000
Relinquishment Payments [Abstract]
Principal		0	0	$ 24,400,000
Accretion of discount	[1]	0	0	778,000
Total relinquishment payments		0	0	25,200,000
Relinquishment liability reassessment		$ 0	$ 0	$ 243,000

[1] Reflects accretion of the discount to the present value of the relinquishment liability for the impact of the time value of money.