CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Capital in Excess of Par Value	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Total
Balance at Dec. 31, 2016	$ 21,749		$ 803,152	$ (18,102)	$ 806,799
Balance (in shares) at Dec. 31, 2016	217,489,000
Increase (Decrease) in Stockholders' Equity
Stock issued for stock incentive plans, net	$ 42	$ 11,048			11,090
Stock issued for stock incentive plans, net (in shares)	420,000
Stock purchased and retired	$ (137)	(11,048)	(15,599)		(26,784)
Stock purchased and retired (in shares)	(1,365,000)
Net (loss) income			162,511		162,511
Pension adjustment, net of taxes				1,033	1,033
Foreign currency translation				391	391
Unrealized loss on securities; net of taxes and reclassification adjustment				(24)	(24)
Dividends declared			(43,319)		(43,319)
Balance at Dec. 31, 2017	$ 21,654		906,745	(16,702)	911,697
Balance (in shares) at Dec. 31, 2017	216,544,000
Increase (Decrease) in Stockholders' Equity
Stock issued for stock incentive plans, net	$ 37	9,382			9,419
Stock issued for stock incentive plans, net (in shares)	367,000
Stock purchased and retired	$ (237)	(9,382)	(33,382)		(43,001)
Stock purchased and retired (in shares)	(2,367,000)
Net (loss) income			175,402		175,402
Pension adjustment, net of taxes				(1,408)	(1,408)
Foreign currency translation				(621)	(621)
Dividends declared			(101,069)		(101,069)
Balance at Dec. 31, 2018	$ 21,454		947,711	(18,746)	$ 950,419
Balance (in shares) at Dec. 31, 2018	214,544,000				214,543,511
Increase (Decrease) in Stockholders' Equity
Adoption of accounting standard (Note 1)			15	(15)
Stock issued for stock incentive plans, net	$ 66	8,564			$ 8,630
Stock issued for stock incentive plans, net (in shares)	667,000
Stock purchased and retired	$ (77)	$ (8,564)	1,280		(7,361)
Stock purchased and retired (in shares)	(788,000)
Net (loss) income			(87,111)		(87,111)
Pension adjustment, net of taxes				(2,298)	(2,298)
Foreign currency translation				553	553
Dividends declared			(32,231)		(32,231)
Balance at Dec. 31, 2019	$ 21,443		832,113	(23,223)	$ 830,333
Balance (in shares) at Dec. 31, 2019	214,423,000				214,422,979
Increase (Decrease) in Stockholders' Equity
Adoption of accounting standard (Note 1)			$ 2,464	$ (2,732)	$ (268)