CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - 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, 2017	$ 21,654		$ 906,745	$ (16,702)	$ 911,697
Balance (in shares) at Dec. 31, 2017	216,544
Increase (Decrease) in Stockholders' Equity
Stock issued for stock incentive plans, net	$ 50	$ 2,505			2,555
Stock issued for stock incentive plans, net (in shares)	498
Stock purchased and retired	$ (157)	(2,505)	(28,048)		(30,710)
Stock purchased and retired (in shares)	(1,573)
Net (loss) income			52,130		52,130
Dividends			(21,657)		(21,657)
Pension adjustment, net of taxes				173	173
Foreign currency translation				(481)	(481)
Balance at Mar. 31, 2018	$ 21,547		909,185	(17,025)	913,707
Balance (in shares) at Mar. 31, 2018	215,469
Balance at Dec. 31, 2017	$ 21,654		906,745	(16,702)	911,697
Balance (in shares) at Dec. 31, 2017	216,544
Increase (Decrease) in Stockholders' Equity
Net (loss) income					162,040
Foreign currency translation					(29)
Balance at Sep. 30, 2018	$ 21,480		971,382	(16,261)	976,601
Balance (in shares) at Sep. 30, 2018	214,798
Increase (Decrease) in Stockholders' Equity
Adoption of accounting standards (Note 2)			15	(15)
Balance at Mar. 31, 2018	$ 21,547		909,185	(17,025)	913,707
Balance (in shares) at Mar. 31, 2018	215,469
Increase (Decrease) in Stockholders' Equity
Stock issued for stock incentive plans, net	$ (8)	2,039			2,031
Stock issued for stock incentive plans, net (in shares)	(82)
Stock purchased and retired	$ (56)	(2,039)	(7,291)		(9,386)
Stock purchased and retired (in shares)	(560)
Net (loss) income			59,943		59,943
Dividends			(21,529)		(21,529)
Pension adjustment, net of taxes				155	155
Foreign currency translation				66	66
Balance at Jun. 30, 2018	$ 21,483		940,308	(16,804)	944,987
Balance (in shares) at Jun. 30, 2018	214,827
Increase (Decrease) in Stockholders' Equity
Stock issued for stock incentive plans, net	$ (3)	2,621			2,618
Stock issued for stock incentive plans, net (in shares)	(25)
Stock purchased and retired	$ 0	(2,621)	2,557		(64)
Stock purchased and retired (in shares)	(4)
Net (loss) income			49,967		49,967
Dividends			(21,450)		(21,450)
Pension adjustment, net of taxes				157	157
Foreign currency translation				386	386
Balance at Sep. 30, 2018	$ 21,480		971,382	(16,261)	976,601
Balance (in shares) at Sep. 30, 2018	214,798
Balance at Dec. 31, 2018	$ 21,454		947,711	(18,746)	950,419
Balance (in shares) at Dec. 31, 2018	214,544
Increase (Decrease) in Stockholders' Equity
Stock issued for stock incentive plans, net	$ 84	2,368			2,452
Stock issued for stock incentive plans, net (in shares)	843
Stock purchased and retired	$ (24)	(2,368)	(306)		(2,698)
Stock purchased and retired (in shares)	(245)
Net (loss) income			(739)		(739)
Dividends			(21,486)		(21,486)
Pension adjustment, net of taxes				173	173
Foreign currency translation				98	98
Balance at Mar. 31, 2019	$ 21,514		927,556	(21,207)	927,863
Balance (in shares) at Mar. 31, 2019	215,142
Balance at Dec. 31, 2018	$ 21,454		947,711	(18,746)	950,419
Balance (in shares) at Dec. 31, 2018	214,544
Increase (Decrease) in Stockholders' Equity
Net (loss) income					(63,749)
Foreign currency translation					513
Balance at Sep. 30, 2019	$ 21,450		854,170	(20,445)	855,175
Balance (in shares) at Sep. 30, 2019	214,500
Increase (Decrease) in Stockholders' Equity
Adoption of accounting standards (Note 2)			2,376	(2,732)	(356)
Balance at Mar. 31, 2019	$ 21,514		927,556	(21,207)	927,863
Balance (in shares) at Mar. 31, 2019	215,142
Increase (Decrease) in Stockholders' Equity
Stock issued for stock incentive plans, net	$ (2)	2,438			2,436
Stock issued for stock incentive plans, net (in shares)	(23)
Stock purchased and retired	$ (54)	(2,438)	(2,159)		(4,651)
Stock purchased and retired (in shares)	(540)
Net (loss) income			6,171		6,171
Dividends			(10,738)		(10,738)
Pension adjustment, net of taxes				174	174
Foreign currency translation				333	333
Balance at Jun. 30, 2019	$ 21,458		920,917	(20,700)	921,675
Balance (in shares) at Jun. 30, 2019	214,579
Increase (Decrease) in Stockholders' Equity
Adoption of accounting standards (Note 2)			87		87
Stock issued for stock incentive plans, net	$ (8)	2,444			2,436
Stock issued for stock incentive plans, net (in shares)	(77)
Stock purchased and retired		$ (2,444)	2,434		(10)
Stock purchased and retired (in shares)	(2)
Net (loss) income			(69,181)		(69,181)
Pension adjustment, net of taxes				173	173
Foreign currency translation				82	82
Balance at Sep. 30, 2019	$ 21,450		$ 854,170	$ (20,445)	$ 855,175
Balance (in shares) at Sep. 30, 2019	214,500