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, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 292,721	[1]	$ 272,688	[1]	$ 253,161	[1]	$ 245,093	[1]	$ 252,525	[1]	$ 178,603	[1]	$ 171,621	[1]	$ 184,672	[1]	$ 1,063,663	$ 787,421	$ 645,076
Income before income taxes	118,152	[1]	105,130	[1]	97,432	[1]	84,087	[1]	109,891	[1]	61,990	[1]	63,492	[1]	77,931	[1]	404,801	313,304	324,847
Net income	$ 101,893	[1]	$ 89,981	[1]	$ 85,519	[1]	$ 72,831	[1]	$ 95,526	[1]	$ 51,711	[1]	$ 59,466	[1]	$ 65,468	[1]	$ 350,224	$ 272,171	$ 271,674
Basic (in dollars per share)	$ 1.59	[1]	$ 1.38	[1]	$ 1.30	[1]	$ 1.11	[1]	$ 1.46	[1]	$ 0.79	[1]	$ 0.91	[1]	$ 1.01	[1]	$ 5.38	$ 4.17	$ 4.20
Diluted (in dollars per share)	$ 1.57	[1]	$ 1.37	[1]	$ 1.28	[1]	$ 1.10	[1]	$ 1.45	[1]	$ 0.79	[1]	$ 0.90	[1]	$ 1.00	[1]	$ 5.32	$ 4.14	$ 4.15

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