Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Capital in Excess of Par Value	Retained Earnings	Accumulated Other Comprehensive (Loss) Income
Beginning balance at Dec. 31, 2022	$ 1,165,826	$ 347	$ 646,237	$ 668,882	$ (149,640)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	230,377			230,377
Actuarially determined long-term liability adjustments	(901)				(901)
Investments in available-for-sale securities	212				212
Comprehensive Income (Loss)	229,688			230,377	(689)
Issuance of Common Stock	0	3	(3)
Repurchases of common stock	(67,133)	(11)	(22,446)	(44,676)
Excise Tax on Repurchases of Common Stock	(478)			(478)
Employee Stock-Based Compensation	4,792		4,792
Shares Withheld for Taxes	(12,708)		(12,708)
Dividends on common shares	(38,287)			(38,287)
Dividend Equivalents Earned on Stock-Based Compensation Awards	(803)			(803)
Ending balance at Mar. 31, 2023	1,280,897	339	615,872	815,015	(150,329)
Beginning balance at Dec. 31, 2022	1,165,826	347	646,237	668,882	(149,640)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	498,825
Actuarially determined long-term liability adjustments	(2,702)
Investments in available-for-sale securities	(49)
Comprehensive Income (Loss)	496,074
Ending balance at Sep. 30, 2023	1,308,790	312	569,071	891,798	(152,391)
Beginning balance at Mar. 31, 2023	1,280,897	339	615,872	815,015	(150,329)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	167,723			167,723
Actuarially determined long-term liability adjustments	(900)				(900)
Investments in available-for-sale securities	(255)				(255)
Comprehensive Income (Loss)	166,568			167,723	(1,155)
Repurchases of common stock	(75,627)	(12)	(22,261)	(53,354)
Excise Tax on Repurchases of Common Stock	(728)			(728)
Employee Stock-Based Compensation	1,993		1,993
Shares Withheld for Taxes	(38)		(38)
Dividends on common shares	(37,187)			(37,187)
Dividend Equivalents Earned on Stock-Based Compensation Awards	(683)			(683)
Ending balance at Jun. 30, 2023	1,335,195	327	595,566	890,786	(151,484)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	100,725			100,725
Actuarially determined long-term liability adjustments	(901)				(901)
Investments in available-for-sale securities	(6)				(6)
Comprehensive Income (Loss)	99,818			100,725	(907)
Repurchases of common stock	(126,634)	(15)	(28,171)	(98,448)
Excise Tax on Repurchases of Common Stock	(1,265)			(1,265)
Employee Stock-Based Compensation	1,676		1,676
Ending balance at Sep. 30, 2023	1,308,790	312	569,071	891,798	(152,391)
Beginning balance at Dec. 31, 2023	1,343,442	299	547,861	944,342	(149,060)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	101,891			101,891
Actuarially determined long-term liability adjustments	385				385
Investments in available-for-sale securities	(126)				(126)
Comprehensive Income (Loss)	102,150			101,891	259
Issuance of Common Stock	0	1	(1)
Repurchases of common stock	(55,881)	(6)	(11,264)	(44,611)
Excise Tax on Repurchases of Common Stock	(471)			(471)
Employee Stock-Based Compensation	5,129		5,118	11
Shares Withheld for Taxes	(5,551)		(5,551)
Ending balance at Mar. 31, 2024	1,388,818	294	536,163	1,001,162	(148,801)
Beginning balance at Dec. 31, 2023	1,343,442	299	547,861	944,342	(149,060)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	255,584
Actuarially determined long-term liability adjustments	1,155
Investments in available-for-sale securities	95
Comprehensive Income (Loss)	256,834
Ending balance at Sep. 30, 2024	1,529,495	294	538,054	1,138,957	(147,810)
Beginning balance at Mar. 31, 2024	1,388,818	294	536,163	1,001,162	(148,801)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	58,061			58,061
Actuarially determined long-term liability adjustments	385				385
Investments in available-for-sale securities	(17)				(17)
Comprehensive Income (Loss)	58,429			58,061	368
Issuance of Common Stock	0	1	(1)
Repurchases of common stock	(10,997)	(1)	(2,407)	(8,589)
Excise Tax on Repurchases of Common Stock	(82)			(82)
Employee Stock-Based Compensation	2,262		2,237	25
Shares Withheld for Taxes	(27)		(27)
Ending balance at Jun. 30, 2024	1,438,403	294	535,965	1,050,577	(148,433)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	95,632			95,632
Actuarially determined long-term liability adjustments	385				385
Investments in available-for-sale securities	238				238
Comprehensive Income (Loss)	96,255			95,632	623
Excise Tax on Repurchases of Common Stock	2			2
Employee Stock-Based Compensation	2,252		2,051	201
Shares Withheld for Taxes	38		38
Dividends on common shares	(7,348)			(7,348)
Dividend Equivalents Earned on Stock-Based Compensation Awards	(107)			(107)
Ending balance at Sep. 30, 2024	$ 1,529,495	$ 294	$ 538,054	$ 1,138,957	$ (147,810)