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, 2014	$ 21,654		$ 1,074,561	$ (17,833)	$ 1,078,382
Balance (in shares) at Dec. 31, 2014	216,539,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock issued for stock incentive plans, net	$ 79	$ 9,802			9,881
Stock issued for stock incentive plans, net (in shares)	791,000
Stock purchased and retired	$ (34)	(11,212)	7,153		(4,093)
Stock purchased and retired (in shares)	(339,000)
Net income (loss)			(99,561)		(99,561)
Pension adjustment, net of taxes				1,531	1,531
Foreign currency translation				(1,801)	(1,801)
Unrealized gain (loss) on securities, net of taxes and reclassification adjustment				134	134
Dividends declared			(33,602)		(33,602)
Excess tax benefits for share- based payments		1,410			1,410
Balance at Dec. 31, 2015	$ 21,699		948,551	(17,969)	952,281
Balance (in shares) at Dec. 31, 2015	216,991,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock issued for stock incentive plans, net	$ 80	9,508			9,588
Stock issued for stock incentive plans, net (in shares)	796,000
Stock purchased and retired	$ (30)	(9,935)	6,708		(3,257)
Stock purchased and retired (in shares)	(298,000)
Net income (loss)			(141,246)		(141,246)
Pension adjustment, net of taxes				(788)	(788)
Foreign currency translation				652	652
Unrealized gain (loss) on securities, net of taxes and reclassification adjustment				3	3
Dividends declared			(10,861)		(10,861)
Excess tax benefits for share- based payments		427			427
Balance at Dec. 31, 2016	$ 21,749		803,152	(18,102)	$ 806,799
Balance (in shares) at Dec. 31, 2016	217,489,000				217,489,402
Increase (Decrease) in Stockholders' Equity [Roll Forward]
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 income (loss)			162,511		162,511
Pension adjustment, net of taxes				1,033	1,033
Foreign currency translation				391	391
Unrealized gain (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				216,543,552