Statement of Shareholders Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock [Member]	Retained Earnings [Member]	Treasury Stock [Member]
Beginning Balance at Dec. 31, 2011	$ 1,593,709	$ 463,221	$ 1,145,439	$ (14,951)
Beginning Balance, Shares at Dec. 31, 2011		152,477,000
Stock options exercised	632	632
Stock options exercised, Shares		34,000
Employee stock plan grants	613	613		0
Employee stock plan grants, Shares		708,000
Shares re-issued from treasury	0	(1,245)	(14,793)	16,038
Shares repurchased	(1,100)			(1,100)
Shares repurchased, Shares		(50,000)
Net share settlements	(5,618)		(5,618)
Net share settlements, Shares		(239,000)
Fair value of employee stock plan grants	15,222	15,222
Tax benefit of stock options exercised	(4,427)	(4,427)
Comprehensive earnings:
Net earnings (loss)	(2,176,898)		(2,176,898)
Ending Balance at Dec. 31, 2012	(577,867)	474,016	(1,051,870)	(13)
Ending Balance, Shares at Dec. 31, 2012		152,930,000
Stock options exercised	11	11
Stock options exercised, Shares		1,000
Employee stock plan grants	700	700
Employee stock plan grants, Shares		347,000
Shares re-issued from treasury	0	(711)	(652)	1,363
Shares repurchased	(3,311)			(3,311)
Shares repurchased, Shares		(165,000)
Net share settlements	(2,118)		(2,118)
Net share settlements, Shares		(122,000)
Fair value of employee stock plan grants	13,257	13,257
Comprehensive earnings:
Net earnings (loss)	237,838		237,838
Ending Balance at Dec. 31, 2013	(331,490)	487,273	(816,802)	(1,961)
Ending Balance, Shares at Dec. 31, 2013		152,991,000
Stock options exercised	770	770
Stock options exercised, Shares		43,000
Employee stock plan grants	700	700
Employee stock plan grants, Shares		298,000
Shares re-issued from treasury	0	(770)	(1,450)	2,220
Shares repurchased	(6,472)			(6,472)
Shares repurchased, Shares		(332,000)
Net share settlements	(2,639)		(2,639)
Net share settlements, Shares		(104,000)
Fair value of employee stock plan grants	7,940	7,940
Comprehensive earnings:
Net earnings (loss)	542,851		542,851
Ending Balance at Dec. 31, 2014	$ 211,660	$ 495,913	$ (278,040)	$ (6,213)
Ending Balance, Shares at Dec. 31, 2014		152,896,000