QUARTERLY FINANCIAL DATA (UNAUDITED) (Schedule of Quarterly Financial Information) (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
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 188,677	$ 227,797	$ 296,351	$ 307,819	$ 363,176	$ 330,562	$ 350,387	$ 351,726	$ 1,020,644	$ 1,395,851	$ 1,173,953
Gross profit	105,843	141,784	197,310	168,881	235,492	187,238	210,602	203,354
Income before income taxes	5,918	120,116	136,426	50,295	166,115	122,539	134,976	55,340	312,755	478,970	397,293
Net income	$ 4,249	$ 99,505	$ 122,437	$ 39,081	$ 150,694	$ 112,992	$ 122,669	$ 46,218	$ 265,272	$ 432,573	$ 340,822
Earnings per common share:
Basic (in dollars per share)	$ 0.07	$ 1.54	$ 1.89	$ 0.60	$ 2.33	$ 1.75	$ 1.90	$ 0.72	$ 4.09	$ 6.70	$ 5.31
Diluted (in dollars per share)	$ 0.07	$ 1.53	$ 1.89	$ 0.60	$ 2.32	$ 1.73	$ 1.89	$ 0.71	$ 4.09	$ 6.65	$ 5.24