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, 2019		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		27,491,000
Balance at Jun. 30, 2019	726,873	$ 122,844	1,359,782	(10,308)	(745,445)
Net income	84,169
Net pension and postretirement benefit gains, net of tax effect	139
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)
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)
Balance (in shares) at Jun. 30, 2020	27,523,935	27,524,000
Balance at Jun. 30, 2020	$ 783,300	$ 125,153	1,421,121	(12,070)	(750,904)
Net income	37,079		37,079
Net pension and postretirement benefit gains, net of tax effect	94			94
Cash dividends - common stock	(19,270)		(19,270)
Purchase of treasury stock (in shares)		0
Purchase of treasury stock	(15)				(15)
Stock-based plans (in shares)		16,000
Stock-based plans	(1,854)	$ (1,854)
Stock-based compensation expense	1,772	$ 1,772
Balance (in shares) at Sep. 30, 2020		27,540,000
Balance at Sep. 30, 2020	$ 801,106	$ 125,071	1,438,930	(11,976)	(750,919)
Balance (in shares) at Jun. 30, 2020	27,523,935	27,524,000
Balance at Jun. 30, 2020	$ 783,300	$ 125,153	1,421,121	(12,070)	(750,904)
Net income	81,709
Net pension and postretirement benefit gains, net of tax effect	$ 188
Balance (in shares) at Dec. 31, 2020	27,547,331	27,547,000
Balance at Dec. 31, 2020	$ 826,360	$ 126,260	1,462,905	(11,882)	(750,923)
Balance (in shares) at Sep. 30, 2020		27,540,000
Balance at Sep. 30, 2020	801,106	$ 125,071	1,438,930	(11,976)	(750,919)
Net income	44,630		44,630
Net pension and postretirement benefit gains, net of tax effect	94			94
Cash dividends - common stock	(20,655)		(20,655)
Purchase of treasury stock (in shares)		0
Purchase of treasury stock	(4)				(4)
Stock-based plans (in shares)		7,000
Stock-based plans	(581)	$ (581)
Stock-based compensation expense	$ 1,770	$ 1,770
Balance (in shares) at Dec. 31, 2020	27,547,331	27,547,000
Balance at Dec. 31, 2020	$ 826,360	$ 126,260	$ 1,462,905	$ (11,882)	$ (750,923)