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, 2015	$ 1,955,679	$ 133,696	$ 1,643,712	$ 829,754	$ 353	$ (651,836)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	35,098			35,098
Other comprehensive income (loss)	(4,785)				(4,785)
Dividends on common stock	(12,036)			(12,036)
Compensation expense related to common stock options	300		300
Proceeds from exercise of common stock options	5,042	227	4,815
Restricted stock expense	880	178	702
Treasury stock acquired	(9,938)					(9,938)
Balance, end of period at Dec. 31, 2015	1,970,240	134,101	1,649,529	852,816	(4,432)	(661,774)
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	41,246			41,246
Other comprehensive income (loss)	8,324				8,324
Dividends on common stock	(12,422)			(12,422)
Proceeds from exercise of common stock options	4,362	190	4,172
Restricted stock expense	2,745	109	2,636
Exercise of stock warrants	0	50	(50)
Treasury stock acquired	(20,385)					(20,385)
Balance, end of period at Dec. 31, 2016	$ 1,999,601	$ 134,657	$ 1,655,146	$ 972,701	$ (2,832)	$ (760,071)