CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (USD $) In Thousands, unless otherwise specified	Total	Common Stock [Member]	Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Beginning Balance at Sep. 30, 2009	$ 1,102,293	$ 64,236	$ 122,457	$ 915,600	$ 0
Beginning Balance (in shares) at Sep. 30, 2009		64,236
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	256,996			256,996
Other comprehensive loss	0
Restricted stock awards		145	(145)
Restricted stock awards (in shares)		145
Exercise of employee stock options	847	62	785
Exercise of employee stock options (in shares)		62
Stock option and restricted stock award compenstion expense	9,998		9,998
Ending Balance at Sep. 30, 2010	1,370,134	64,443	133,095	1,172,596	0
Ending Balance (in shares) at Sep. 30, 2010		64,443
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	271,674			271,674
Other comprehensive loss	(1,527)				(1,527)
Restricted stock awards		102	(102)
Restricted stock awards (in shares)		102
Exercise of employee stock options	6,192	415	5,777
Exercise of employee stock options (in shares)		415
Stock option and restricted stock award compenstion expense	6,314		6,314
Ending Balance at Sep. 30, 2011	1,652,787	64,960	145,084	1,444,270	(1,527)
Ending Balance (in shares) at Sep. 30, 2011		64,960
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	272,171
Other comprehensive loss	(1,484)				(1,484)
Restricted stock awards		207	(207)
Restricted stock awards (in shares)		207
Exercise of employee stock options	5,546	285	5,261
Exercise of employee stock options (in shares)	285	285
Stock option and restricted stock award compenstion expense	10,402		10,402
Ending Balance at Sep. 30, 2012	$ 1,939,422	$ 65,452	$ 160,540	$ 1,716,441	$ (3,011)
Ending Balance (in shares) at Sep. 30, 2012		65,452