SUMMARY OF QUARTERLY RESULTS OF OPERATIONS (UNAUDITED) (Details 2) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Summary Of quarterly results of operations
Increase (decrease) in operating income	$ 34,709	$ 10,293	$ 23,206	$ 7,179	$ 39,268	$ 19,215	$ 22,177	$ 11,830	$ 75,387	$ 92,490	$ 40,735
Increase (decrease) in net income									$ 22,914	$ 69,580	$ 25,269
Increase (decrease) in net income per common share (in dollars per share)	$ 0.74	$ 0.33	$ (0.41)	$ 0.19	$ 1.22	$ 0.46	$ 0.60	$ 0.31	$ 0.85	$ 2.59	$ 0.94
Change in estimated total costs | Adjustment
Summary Of quarterly results of operations
Increase (decrease) in operating income	$ 700				$ 10,700				$ (14,500)	$ 1,300	$ (1,700)
Increase (decrease) in net income	$ 500				$ 7,600				$ (8,000)	$ 3,500	$ (300)
Increase (decrease) in net income per common share (in dollars per share)	$ 0.02				$ 0.28				$ (0.30)	$ 0.13	$ (0.01)