Statements Of Consolidated Shareholders' Equity (USD $) In Thousands, except Share data	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Repurchased Common Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance at Dec. 31, 2009		$ 38,971	$ 567,584	$ 890,915	$ (575,219)	$ (235,522)
Balance, shares at Dec. 31, 2009		62,512,456
Net Income	3,985			3,985
Foreign currency translation adjustment	(913)					(913)
Employee benefit plans, net of derferred tax	(43,488)					(43,488)
Unrealized gain (loss) on available-for-sale security, net of deferred tax	29					29
Exercise of stock options, including tax benefits		104	2,958
Exercise of stock options, including tax benefits, shares		165,480
Share-based compensation, net of tax		68	11,594	(64)	(713)
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures		73,058
Repurchased common stock issued for 401k match			(2,128)	(10,025)	48,916
Common stock offering				(42,779)	186,104
Common dividends declared				(20,845)
Balance at Dec. 31, 2010		39,143	580,008	821,187	(340,912)	(279,894)
Balance, shares at Dec. 31, 2010		62,750,994
Net Income	88,443			88,443
Foreign currency translation adjustment	(1,331)					(1,331)
Employee benefit plans, net of derferred tax	(157,205)					(157,205)
Unrealized gain (loss) on available-for-sale security, net of deferred tax	(6)					(6)
Exercise of stock options, including tax benefits		153	6,008
Exercise of stock options, including tax benefits, shares		244,944
Share-based compensation, net of tax		98	9,976	(73)	(1,471)
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures		69,993
Repurchased common stock issued for 401k match				(2,622)	19,929
Common dividends declared				(22,177)	0
Balance at Dec. 31, 2011	759,254	39,394	595,992	884,758	(322,454)	(438,436)
Balance, shares at Dec. 31, 2011		63,065,931
Net Income	104,546			104,546
Foreign currency translation adjustment	481					481
Employee benefit plans, net of derferred tax	(18,732)					(18,732)
Unrealized gain (loss) on available-for-sale security, net of deferred tax	226					226
Exercise of stock options, including tax benefits		94	3,631
Exercise of stock options, including tax benefits, shares		150,213
Share-based compensation, net of tax		213	14,711	(8)	(3,674)
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures		349,309
Common dividends declared				(22,357)
Balance at Dec. 31, 2012	$ 838,385	$ 39,701	$ 614,334	$ 966,939	$ (326,128)	$ (456,461)
Balance, shares at Dec. 31, 2012		63,565,453