Consolidated Statements of Shareholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Common stock, without par value	Retained earnings	Additional paid-in capital	Accumulated other comprehensive income (loss)
Balance, beginning of year at Sep. 30, 2011		$ 60,259	$ 212,096	$ 468,323	$ (21,833)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	87,898		87,898
Cash dividends — Common Stock			(70,615)
Dividends of net assets			0
Excess tax benefits on equity-based compensation				369
Net gains (losses) on derivative instruments	(6,744)				(6,744)
Reclassifications of net losses on derivative instruments	1,111				1,111
Benefit plans, principally actuarial (losses) gains					(2,745)
Reclassifications of benefit plans actuarial losses and prior service costs	394				394
Balance, end of year at Sep. 30, 2012	728,513	60,259	229,379	468,692	(29,817)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	102,098		102,098
Cash dividends — Common Stock			(58,975)
Dividends of net assets			(2,525)
Excess tax benefits on equity-based compensation				1,406
Net gains (losses) on derivative instruments	15,153				15,153
Reclassifications of net losses on derivative instruments	471				471
Benefit plans, principally actuarial (losses) gains					4,689
Reclassifications of benefit plans actuarial losses and prior service costs	784				784
Balance, end of year at Sep. 30, 2013	791,614	60,259	269,977	470,098	(8,720)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	124,106		124,106
Cash dividends — Common Stock			(77,395)
Dividends of net assets			0
Excess tax benefits on equity-based compensation				973
Net gains (losses) on derivative instruments	0				0
Reclassifications of net losses on derivative instruments	1,567				1,567
Benefit plans, principally actuarial (losses) gains					(1,413)
Reclassifications of benefit plans actuarial losses and prior service costs	385				385
Balance, end of year at Sep. 30, 2014	$ 839,837	$ 60,259	$ 316,688	$ 471,071	$ (8,181)