QUARTERLY FINANCIAL DATA (UNAUDITED) (Schedule of Quarterly Financial Information) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 323,373	[1]	$ 292,777	[1]	$ 273,097	[1]	$ 284,706	[1]	$ 292,721	[1]	$ 272,688	[1]	$ 253,161	[1]	$ 245,093	[1]	$ 1,173,953	$ 1,063,663	$ 787,421
Income before income taxes	126,385	[1]	79,365	[1]	97,283	[1]	94,260	[1]	118,152	[1]	105,130	[1]	97,432	[1]	84,087	[1]	397,293	404,801	313,304
Net income	$ 112,200	[1]	$ 71,925	[1]	$ 73,300	[1]	$ 83,397	[1]	$ 101,893	[1]	$ 89,981	[1]	$ 85,519	[1]	$ 72,831	[1]	$ 340,822	$ 350,224	$ 272,171
Earnings per common share:
Basic (in dollars per share)	$ 1.74	[1]	$ 1.12	[1]	$ 1.14	[1]	$ 1.30	[1]	$ 1.59	[1]	$ 1.38	[1]	$ 1.30	[1]	$ 1.11	[1]	$ 5.31	$ 5.38	$ 4.17
Diluted (in dollars per share)	$ 1.72	[1]	$ 1.11	[1]	$ 1.13	[1]	$ 1.28	[1]	$ 1.57	[1]	$ 1.37	[1]	$ 1.28	[1]	$ 1.10	[1]	$ 5.24	$ 5.32	$ 4.14

[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.