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, 2018		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		27,488,000
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		27,505,000
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		27,505,000
Balance at Mar. 31, 2019	$ 715,008	$ 121,565	1,344,638	(8,129)	(743,066)
Balance (in shares) at Jun. 30, 2019	27,491,497	27,491,000
Balance at Jun. 30, 2019	$ 726,873	$ 122,844	1,359,782	(10,308)	(745,445)
Net income	40,745		40,745
Net pension and postretirement benefit gains, net of tax effect	70			70
Cash dividends - common stock	(17,869)		(17,869)
Purchase of treasury stock (in shares)		(10,000)
Purchase of treasury stock	(1,465)				(1,465)
Stock-based plans (in shares)		4,000
Stock-based plans	(125)	$ (125)
Stock-based compensation expense	1,436	$ 1,436
Balance (in shares) at Sep. 30, 2019		27,485,000
Balance at Sep. 30, 2019	$ 749,665	$ 124,155	1,382,658	(10,238)	(746,910)
Balance (in shares) at Jun. 30, 2019	27,491,497	27,491,000
Balance at Jun. 30, 2019	$ 726,873	$ 122,844	1,359,782	(10,308)	(745,445)
Net income	106,598
Net pension and postretirement benefit gains, net of tax effect	$ 209
Balance (in shares) at Mar. 31, 2020	27,515,651	27,516,000
Balance at Mar. 31, 2020	$ 773,284	$ 124,221	1,409,994	(10,099)	(750,832)
Balance (in shares) at Sep. 30, 2019		27,485,000
Balance at Sep. 30, 2019	749,665	$ 124,155	1,382,658	(10,238)	(746,910)
Net income	43,424		43,424
Net pension and postretirement benefit gains, net of tax effect	69			69
Cash dividends - common stock	(19,245)		(19,245)
Purchase of treasury stock (in shares)		0
Purchase of treasury stock	(7)				(7)
Stock-based plans (in shares)		26,000
Stock-based plans	(2,571)	$ (2,571)
Stock-based compensation expense	1,423	$ 1,423
Balance (in shares) at Dec. 31, 2019		27,511,000
Balance at Dec. 31, 2019	772,758	$ 123,007	1,406,837	(10,169)	(746,917)
Net income	22,429		22,429
Net pension and postretirement benefit gains, net of tax effect	70			70
Cash dividends - common stock	(19,272)		(19,272)
Purchase of treasury stock (in shares)		(28,000)
Purchase of treasury stock	(3,915)				(3,915)
Stock-based plans (in shares)		33,000
Stock-based plans	(264)	$ (264)
Stock-based compensation expense	$ 1,478	$ 1,478
Balance (in shares) at Mar. 31, 2020	27,515,651	27,516,000
Balance at Mar. 31, 2020	$ 773,284	$ 124,221	$ 1,409,994	$ (10,099)	$ (750,832)