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, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2010		Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010
Quarterly Financial Data [Abstract]
Revenues	$ 252,525	[1]	$ 178,603	[1]	$ 171,621	[1]	$ 184,672	[1]	$ 177,558	[1]	$ 162,147	[1]	$ 159,085	[1]	$ 146,286	[1]	$ 787,421	$ 645,076	$ 650,562
Income before income taxes	109,891	[1]	61,990	[1]	63,492	[1]	77,931	[1]	83,919	[1]	87,203	[1]	90,485	[1]	63,240	[1]	313,304	324,847	319,979
Net income	$ 95,526	[1]	$ 51,711	[1]	$ 59,466	[1]	$ 65,468	[1]	$ 72,928	[1]	$ 75,285	[1]	$ 70,611	[1]	$ 52,850	[1]	$ 272,171	$ 271,674	$ 256,996
Basic (in dollars per share)	$ 1.46	[1]	$ 0.79	[1]	$ 0.91	[1]	$ 1.01	[1]	$ 1.13	[1]	$ 1.16	[1]	$ 1.09	[1]	$ 0.82	[1]	$ 4.17	$ 4.20	$ 3.99
Diluted (in dollars per share)	$ 1.45	[1]	$ 0.79	[1]	$ 0.90	[1]	$ 1.00	[1]	$ 1.12	[1]	$ 1.15	[1]	$ 1.08	[1]	$ 0.81	[1]	$ 4.14	$ 4.15	$ 3.95

[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.