SUMMARY OF QUARTERLY RESULTS OF OPERATIONS (UNAUDITED) - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Summary Of quarterly results of operations
Increase (decrease) in operating income	$ 10,488	$ 13,893	$ (9,086)	$ (8,077)	$ 34,709	$ 10,293	$ 23,206	$ 7,179	$ 7,218	$ 75,387	$ 92,490
Increase (decrease) in net income									$ 1,735	$ 22,914	$ 69,580
Increase (decrease) in net income per common share (in dollars per share)	$ (0.29)	$ 0.17	$ 0.38	$ (0.20)	$ 0.74	$ 0.33	$ (0.41)	$ 0.19	$ 0.06	$ 0.85	$ 2.59
Change in estimated total costs | Adjustment
Summary Of quarterly results of operations
Increase (decrease) in operating income	$ 1,300				$ 700				$ (2,800)	$ (14,500)	$ 1,300
Increase (decrease) in net income	$ 900				$ 500				$ (1,600)	$ (8,000)	$ 3,500
Increase (decrease) in net income per common share (in dollars per share)	$ 0.03				$ 0.02				$ (0.06)	$ (0.30)	$ 0.13