QUARTERLY FINANCIAL DATA (UNAUDITED) (Schedule of Quarterly Financial Information) (Details) - 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
Quarterly Financial Information Disclosure [Abstract]
Revenues		$ 363,176	[1]	$ 330,562	[1]	$ 350,387	[1]	$ 351,726	[1]	$ 323,373	[1]	$ 292,777	[1]	$ 273,097	[1]	$ 284,706	[1]	$ 1,395,851	$ 1,173,953	$ 1,063,663
Gross Profit	[1]	235,492		187,238		210,602		203,354		190,829		140,698		126,943		153,130
Income before income taxes		166,115	[1]	122,539	[1]	134,976	[1]	55,340	[1]	126,385	[1]	79,365	[1]	97,283	[1]	94,260	[1]	478,970	397,293	404,801
Net income		$ 150,694	[1]	$ 112,992	[1]	$ 122,669	[1]	$ 46,218	[1]	$ 112,200	[1]	$ 71,925	[1]	$ 73,300	[1]	$ 83,397	[1]	$ 432,573	$ 340,822	$ 350,224
Earnings per common share:
Basic (in dollars per share)		$ 2.33	[1]	$ 1.75	[1]	$ 1.90	[1]	$ 0.72	[1]	$ 1.74	[1]	$ 1.12	[1]	$ 1.14	[1]	$ 1.30	[1]	$ 6.70	$ 5.31	$ 5.38
Diluted (in dollars per share)		$ 2.32	[1]	$ 1.73	[1]	$ 1.89	[1]	$ 0.71	[1]	$ 1.72	[1]	$ 1.11	[1]	$ 1.13	[1]	$ 1.28	[1]	$ 6.65	$ 5.24	$ 5.32

[1] The sum of the individual quarterly earnings per common share amounts may not agree with year-to-date earnings per common share as each quarterly computation is based on the weighted-average number of common shares outstanding during that period.