CONSOLIDATED STATEMENT OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid In Capital [Member]	Accumulated Other Comprehensive Income [Member]	Retained Earnings [Member]
Common stock shares outstanding, balance at Sep. 30, 2012		90,239,900
Shareholders' equity, beginning balance at Sep. 30, 2012	$ 2,359,243	$ 451	$ 1,745,467	$ (47,607)	$ 660,932
Net income	243,194				243,194
Other comprehensive income (loss)	86,485			86,485
Repurchase of equity awards, shares		(133,449)
Repurchase of equity awards, amount	(5,150)	$ 0	(5,150)
Cash dividends	(128,115)				(128,115)
Common stock issued:
Direct stock purchase plan, shares		0
Direct stock purchase plan, amount	(50)	$ 0	(50)
1998 Long-term incentive plan, shares		531,672
1998 Long-term incentive plan, amount	8,788	$ 2	9,530		(744)
Employee stock-based compensation	15,934		15,934
Outside directors stock-for-fee plan, shares		2,088
Outside directors stock-for-fee-plan, amount	80		80
Common stock shares outstanding, ending balance at Sep. 30, 2013		90,640,211
Shareholders' equity, ending balance at Sep. 30, 2013	2,580,409	$ 453	1,765,811	38,878	775,267
Net income	289,817				289,817
Other comprehensive income (loss)	(51,271)			(51,271)
Repurchase of equity awards, shares		(190,134)
Repurchase of equity awards, amount	(8,717)	$ (1)	(8,716)
Cash dividends	(146,248)				(146,248)
Common stock issued:
Public offering, shares		9,200,000
Public offering, amount	390,205	$ 46	390,159
Direct stock purchase plan, shares		83,150
Direct stock purchase plan, amount	4,067	$ 1	4,066
1998 Long-term incentive plan, shares		653,130
1998 Long-term incentive plan, amount	4,353	$ 3	5,214		(864)
Employee stock-based compensation	23,536		23,536
Outside directors stock-for-fee plan, shares		1,735
Outside directors stock-for-fee-plan, amount	81		81
Common stock shares outstanding, ending balance at Sep. 30, 2014		100,388,092
Shareholders' equity, ending balance at Sep. 30, 2014	3,086,232	$ 502	2,180,151	(12,393)	917,972
Net income	315,075				315,075
Other comprehensive income (loss)	(96,937)			(96,937)
Repurchase of equity awards, shares		(148,464)
Repurchase of equity awards, amount	(7,985)	$ (1)	(7,984)
Cash dividends	(160,018)				(160,018)
Common stock issued:
Direct stock purchase plan, shares		176,391
Direct stock purchase plan, amount	10,626	$ 1	10,625
Retirement savings plan, shares		398,047
Retirement savings plan, amount	20,326	$ 2	20,324
1998 Long-term incentive plan, shares		664,752
1998 Long-term incentive plan, amount	2,266	$ 3	2,263		0
Employee stock-based compensation	25,212		25,212
Common stock shares outstanding, ending balance at Sep. 30, 2015		101,478,818
Shareholders' equity, ending balance at Sep. 30, 2015	$ 3,194,797	$ 507	$ 2,230,591	$ (109,330)	$ 1,073,029