Quarterly Data (unaudited) - Schedule of Quarterly Financial Information (Details) - USD ($) $ 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
Quarterly Financial Data [Abstract]
Revenues	$ 108,172	$ 140,283	$ 322,047	$ 197,982	$ 110,212	$ 143,490	$ 500,573	$ 287,306	$ 768,484	$ 1,041,581	$ 1,086,889
Operating income	8,309	29,815	114,481	48,296	3,144	20,184	142,699	75,640	200,901	241,667	246,400
Net income (loss)	$ (1,875)	$ 12,603	$ 63,294	$ 23,351	$ (4,680)	$ 7,307	$ 79,589	$ 38,839	$ 97,373	$ 121,055	$ 124,106