CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
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	119,825			119,825
Other comprehensive income (loss)	(16,058)				(16,058)
Dividends on common stock	(37,415)			(37,415)
Compensation expense related to common stock options	900		900
Proceeds from exercise of common stock options	6,320	300	6,020
Restricted stock expense	2,982	149	2,833
Treasury stock acquired	(70,048)					(70,048)
Balance, end of period at Jun. 30, 2016	1,962,185	134,145	1,653,465	912,164	(15,705)	(721,884)
Balance, beginning of period at Sep. 30, 2016	1,975,731	134,308	1,648,388	943,877	(11,156)	(739,686)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	127,428			127,428
Other comprehensive income (loss)	13,634				13,634
Dividends on common stock	(61,341)			(61,341)
Proceeds from exercise of common stock options	7,078	309	6,769
Restricted stock expense	5,126	105	5,021
Exercise of stock warrants	0	225	(225)
Treasury stock acquired	(46,470)					(46,470)
Balance, end of period at Jun. 30, 2017	$ 2,021,186	$ 134,947	$ 1,659,953	$ 1,009,964	$ 2,478	$ (786,156)