Statement of Shareholders Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock [Member]	Retained Earnings [Member]	Treasury Stock [Member]
Beginning Balance at Dec. 31, 2009	$ 648,197	$ 377,339	$ 281,383	$ (10,525)
Beginning Balance, Shares at Dec. 31, 2009		151,759
Stock options exercised	6,561	6,561
Stock options exercised, Shares		1,206
Employee stock plan grants	4,841	4,841
Employee stock plan grants, Shares		105
Shares re-issued from treasury	0	(587)	(9,938)	10,525
Net share settlements	(23,707)		(23,707)
Net share settlements, Shares		(502)
Fair value of employee stock plan grants	21,103	21,103
Tax benefit of stock options exercised	17,522	17,522
Comprehensive earnings:
Net earnings (loss)	464,459		464,459
Ending Balance at Dec. 31, 2010	1,138,976	426,779	712,197	0
Ending Balance, Shares at Dec. 31, 2010		152,568
Stock options exercised	9,928	9,928
Stock options exercised, Shares		672
Employee stock plan grants	700	0		700
Employee stock plan grants, Shares		150
Shares re-issued from treasury	0	(686)	(4,531)	5,217
Shares repurchased	(20,868)			(20,868)
Shares repurchased, Shares		(588)
Net share settlements	(15,429)		(15,429)
Net share settlements, Shares		(325)
Fair value of employee stock plan grants	20,988	20,988
Tax benefit of stock options exercised	6,212	6,212
Comprehensive earnings:
Net earnings (loss)	453,202		453,202
Ending Balance at Dec. 31, 2011	1,593,709	463,221	1,145,439	(14,951)
Ending Balance, Shares at Dec. 31, 2011		152,477
Stock options exercised	632	632
Stock options exercised, Shares		34
Employee stock plan grants	613	613
Employee stock plan grants, Shares		708
Shares re-issued from treasury	0	(1,245)	(14,793)	16,038
Shares repurchased	(1,100)			(1,100)
Shares repurchased, Shares		(50)
Net share settlements	(5,618)		(5,618)
Net share settlements, Shares		(239)
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