Condensed Consolidated Statements Of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock Outstanding [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]	Treasury Stock [Member]
Balance (in shares) at Jun. 30, 2017		27,448,000
Balance at Jun. 30, 2017	$ 575,977	$ 115,174	$ 1,206,671	$ (8,936)	$ (736,932)
Net income	29,386		29,386
Net pension and postretirement benefit gains, net of tax effect	56			56
Cash dividends - common stock	(15,092)		(15,092)
Purchase of treasury stock (in shares)		(7,000)
Purchase of treasury stock	(849)				(849)
Stock-based plans (in shares)		1,000
Stock-based plans	(95)	$ (95)
Stock-based compensation expense	1,163	$ 1,163
Balance (in shares) at Sep. 30, 2017		27,442,000
Balance at Sep. 30, 2017	590,546	$ 116,242	1,220,965	(8,880)	(737,781)
Balance (in shares) at Jun. 30, 2017		27,448,000
Balance at Jun. 30, 2017	575,977	$ 115,174	1,206,671	(8,936)	(736,932)
Net income	102,927
Net pension and postretirement benefit gains, net of tax effect	173
Balance (in shares) at Mar. 31, 2018		27,478,000
Balance at Mar. 31, 2018	632,863	$ 118,106	1,263,443	(10,652)	(738,034)
Balance (in shares) at Sep. 30, 2017		27,442,000
Balance at Sep. 30, 2017	590,546	$ 116,242	1,220,965	(8,880)	(737,781)
Net income	45,920		45,920
Net pension and postretirement benefit gains, net of tax effect	55			55
Cash dividends - common stock	(16,469)		(16,469)
Purchase of treasury stock (in shares)		0
Purchase of treasury stock	(4)				(4)
Stock-based plans (in shares)		9,000
Stock-based plans	(189)	$ (189)
Stock-based compensation expense	1,150	$ 1,150
Balance (in shares) at Dec. 31, 2017		27,451,000
Balance at Dec. 31, 2017	621,009	$ 117,203	1,250,416	(8,825)	(737,785)
Net income	27,621		27,621
Net pension and postretirement benefit gains, net of tax effect	62			62
Tax Cuts and Jobs Act of 2017, Reclassification from accumulated other comprehensive loss to retained earnings	0		1,889	(1,889)
Cash dividends - common stock	(16,483)		(16,483)
Purchase of treasury stock (in shares)		(2,000)
Purchase of treasury stock	(249)				(249)
Stock-based plans (in shares)		29,000
Stock-based plans	(268)	$ (268)
Stock-based compensation expense	1,171	$ 1,171
Balance (in shares) at Mar. 31, 2018		27,478,000
Balance at Mar. 31, 2018	$ 632,863	$ 118,106	1,263,443	(10,652)	(738,034)
Balance (in shares) at Jun. 30, 2018	27,487,989	27,488,000
Balance at Jun. 30, 2018	$ 652,282	$ 119,232	1,279,343	(8,259)	(738,034)
Net income	39,028		39,028
Net pension and postretirement benefit gains, net of tax effect	44			44
Cash dividends - common stock	(16,495)		(16,495)
Purchase of treasury stock (in shares)		(10,000)
Purchase of treasury stock	(1,593)				(1,593)
Stock-based plans (in shares)		12,000
Stock-based plans	(778)	$ (778)
Stock-based compensation expense	1,531	$ 1,531
Balance (in shares) at Sep. 30, 2018		27,490,000
Balance at Sep. 30, 2018	$ 674,019	$ 119,985	1,301,876	(8,215)	(739,627)
Balance (in shares) at Jun. 30, 2018	27,487,989	27,488,000
Balance at Jun. 30, 2018	$ 652,282	$ 119,232	1,279,343	(8,259)	(738,034)
Net income	117,539
Net pension and postretirement benefit gains, net of tax effect	$ 130
Balance (in shares) at Mar. 31, 2019	27,504,669	27,505,000
Balance at Mar. 31, 2019	$ 715,008	$ 121,565	1,344,638	(8,129)	(743,066)
Balance (in shares) at Sep. 30, 2018		27,490,000
Balance at Sep. 30, 2018	674,019	$ 119,985	1,301,876	(8,215)	(739,627)
Net income	47,907		47,907
Net pension and postretirement benefit gains, net of tax effect	43			43
Cash dividends - common stock	(17,875)		(17,875)
Purchase of treasury stock (in shares)		(1,000)
Purchase of treasury stock	(166)				(166)
Stock-based plans (in shares)		16,000
Stock-based plans	(988)	$ (988)
Stock-based compensation expense	1,831	$ 1,831
Balance (in shares) at Dec. 31, 2018		27,505,000
Balance at Dec. 31, 2018	704,771	$ 120,828	1,331,908	(8,172)	(739,793)
Net income	30,604		30,604
Net pension and postretirement benefit gains, net of tax effect	43			43
Cash dividends - common stock	(17,874)		(17,874)
Purchase of treasury stock (in shares)		(21,000)
Purchase of treasury stock	(3,273)				(3,273)
Stock-based plans (in shares)		21,000
Stock-based plans	(443)	$ (443)
Stock-based compensation expense	$ 1,180	$ 1,180
Balance (in shares) at Mar. 31, 2019	27,504,669	27,505,000
Balance at Mar. 31, 2019	$ 715,008	$ 121,565	$ 1,344,638	$ (8,129)	$ (743,066)