Condensed Consolidated Statement Of Changes In Equity Statement - USD ($) $ in Thousands	Total	Common Stock	Retained Earnings	Additional Paid-in Capital	AOCI Including Portion Attributable to Noncontrolling Interest
Cumulative effect of change in accounting for employee share-based payments			$ 0
Balance, end of period		$ 60,259	480,858	$ 473,580	$ (26,791)
Balance, beginning of period at Sep. 30, 2017		60,259	480,858	473,580	(26,791)
Tax cuts and jobs act of 2017, reclassification from AOCI to retained earnings, tax effect			0		0
Net income	$ 68,303		68,303
Cash dividends on common stock			(15,000)
Net loss on derivative instruments	0
Reclassifications of net losses on derivatives instruments	592				592
Reclassifications of benefits plans actuarial losses and net prior service costs	220				220
Balance, end of period		60,259	480,858	473,580	(26,791)
Balance, end of period	$ 1,042,021	60,259	534,161	473,580	(25,979)
Common stock, par value (in usd per share)	$ 2.25
Balance, beginning of period at Sep. 30, 2018		60,259	579,778	473,580	(20,329)
Balance, end of period		60,259	579,778	473,580	(20,329)
Cumulative effect of change in accounting for employee share-based payments			(3,926)
Balance, end of period		60,259	579,778	473,580	(20,329)
Common stock, par value (in usd per share)	$ 2.25
Balance, beginning of period at Sep. 30, 2018		60,259	579,778	473,580	(20,329)
Tax cuts and jobs act of 2017, reclassification from AOCI to retained earnings, tax effect			5,451		(5,451)
Net income	$ 49,888		49,888
Cash dividends on common stock			(5,000)
Net loss on derivative instruments	(1,198)				(1,198)
Reclassifications of net losses on derivatives instruments	620				620
Reclassifications of benefits plans actuarial losses and net prior service costs	132				132
Balance, end of period		60,259	579,778	473,580	(20,329)
Balance, end of period	$ 1,133,804	$ 60,259	$ 626,191	$ 473,580	$ (26,226)
Common stock, par value (in usd per share)	$ 2.25