CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Common Stock	Capital in Excess of Par Value	Retained Earnings	Accumulated Other Comprehensive (Loss) Income	Total
Balance at Dec. 31, 2019	$ 21,443		$ 832,113	$ (23,223)	$ 830,333
Balance (in shares) at Dec. 31, 2019	214,423
Increase (Decrease) in Stockholders' Equity
Stock issued for stock incentive plans, net	$ 100	$ 1,997			2,097
Stock issued for stock incentive plans, net (in shares)	1,014
Stock purchased and retired	$ (17)	(1,997)	1,222		(792)
Stock purchased and retired (in shares)	(177)
Net income (loss)			(160,423)		(160,423)
Pension adjustment, net of taxes				732	732
Foreign currency translation				(712)	(712)
Balance at Mar. 31, 2020	$ 21,526		672,912	(23,203)	671,235
Balance (in shares) at Mar. 31, 2020	215,260
Balance at Dec. 31, 2019	$ 21,443		832,113	(23,223)	830,333
Balance (in shares) at Dec. 31, 2019	214,423
Increase (Decrease) in Stockholders' Equity
Net income (loss)					(201,953)
Foreign currency translation					(423)
Balance at Sep. 30, 2020	$ 21,507		638,590	(22,542)	637,555
Balance (in shares) at Sep. 30, 2020	215,067
Balance at Mar. 31, 2020	$ 21,526		672,912	(23,203)	671,235
Balance (in shares) at Mar. 31, 2020	215,260
Increase (Decrease) in Stockholders' Equity
Stock issued for stock incentive plans, net	$ (4)	2,021			2,017
Stock issued for stock incentive plans, net (in shares)	(135)
Stock purchased and retired	$ (10)	(2,021)	2,025		(6)
Stock purchased and retired (in shares)	(2)
Net income (loss)			(25,093)		(25,093)
Pension adjustment, net of taxes				186	186
Foreign currency translation				314	314
Balance at Jun. 30, 2020	$ 21,512		649,844	(22,703)	648,653
Balance (in shares) at Jun. 30, 2020	215,123
Increase (Decrease) in Stockholders' Equity
Stock issued for stock incentive plans, net	$ (5)	5,212			5,207
Stock issued for stock incentive plans, net (in shares)	(54)
Stock purchased and retired		(5,212)	5,183		(29)
Stock purchased and retired (in shares)	(2)
Net income (loss)			(16,437)		(16,437)
Pension adjustment, net of taxes				186	186
Foreign currency translation				(25)	(25)
Balance at Sep. 30, 2020	$ 21,507		638,590	(22,542)	637,555
Balance (in shares) at Sep. 30, 2020	215,067
Balance at Dec. 31, 2020	$ 21,495		627,778	(17,706)	631,567
Balance (in shares) at Dec. 31, 2020	214,951
Increase (Decrease) in Stockholders' Equity
Stock issued for stock incentive plans, net	$ 93	1,446			1,539
Stock issued for stock incentive plans, net (in shares)	924
Stock purchased and retired	$ (14)	(1,446)	903		(557)
Stock purchased and retired (in shares)	(140)
Net income (loss)			(9,662)		(9,662)
Pension adjustment, net of taxes				153	153
Foreign currency translation				136	136
Balance at Mar. 31, 2021	$ 21,574		619,019	(17,417)	623,176
Balance (in shares) at Mar. 31, 2021	215,735
Balance at Dec. 31, 2020	$ 21,495		627,778	(17,706)	631,567
Balance (in shares) at Dec. 31, 2020	214,951
Increase (Decrease) in Stockholders' Equity
Net income (loss)					(5,122)
Foreign currency translation					(34)
Balance at Sep. 30, 2021	$ 21,564		626,501	(17,282)	630,783
Balance (in shares) at Sep. 30, 2021	215,643
Balance at Mar. 31, 2021	$ 21,574		619,019	(17,417)	623,176
Balance (in shares) at Mar. 31, 2021	215,735
Increase (Decrease) in Stockholders' Equity
Stock issued for stock incentive plans, net	$ (1)	1,472			1,471
Stock issued for stock incentive plans, net (in shares)	(9)
Stock purchased and retired		(1,472)	1,463		(9)
Stock purchased and retired (in shares)	(1)
Net income (loss)			(726)		(726)
Pension adjustment, net of taxes				153	153
Foreign currency translation				69	69
Balance at Jun. 30, 2021	$ 21,573		619,756	(17,195)	624,134
Balance (in shares) at Jun. 30, 2021	215,725
Increase (Decrease) in Stockholders' Equity
Stock issued for stock incentive plans, net	$ (9)	1,480			1,471
Stock issued for stock incentive plans, net (in shares)	(82)
Stock purchased and retired		$ (1,480)	1,479		(1)
Net income (loss)			5,266		5,266
Pension adjustment, net of taxes				152	152
Foreign currency translation				(239)	(239)
Balance at Sep. 30, 2021	$ 21,564		$ 626,501	$ (17,282)	$ 630,783
Balance (in shares) at Sep. 30, 2021	215,643