CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Common Stock	Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Balance, beginning of period at Sep. 30, 2014	$ 1,973,283	$ 133,323	$ 1,638,211	$ 706,149	$ 20,708	$ (525,108)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	78,768			78,768
Other comprehensive income (loss)	2,777				2,777
Dividends on common stock	(12,406)			(12,406)
Compensation expense related to common stock options	600		600
Proceeds from exercise of common stock options	492	35	457
Restricted stock expense	1,981	265	1,716
Treasury stock acquired	(77,355)					(77,355)
Balance, end of period at Mar. 31, 2015	1,968,140	133,623	1,640,984	772,511	23,485	(602,463)
Balance, beginning of period at Sep. 30, 2015	1,955,679	133,696	1,643,712	829,754	353	(651,836)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	76,821			76,821
Other comprehensive income (loss)	(8,939)				(8,939)
Dividends on common stock	(24,735)			(24,735)
Compensation expense related to common stock options	600		600
Proceeds from exercise of common stock options	5,399	250	5,149
Restricted stock expense	2,082	146	1,936
Treasury stock acquired	(44,447)					(44,447)
Balance, end of period at Mar. 31, 2016	$ 1,962,460	$ 134,092	$ 1,651,397	$ 881,840	$ (8,586)	$ (696,283)