Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Reconciliation of the numerators and the denominators of basic and diluted per-share computations
Net income - basic and diluted numerator:	$ 201,461	$ 266,586	$ 386,630	$ 517,198
Weighted average shares - basic (denominator):	139,029	139,027	139,028	139,027
Effect of dilutive potential shares
Stock options and stock appreciation rights	11	25	11	25
Weighted average shares including conversions - diluted (denominator)	139,040	139,052	139,039	139,052
Earnings per share:
Basic	$ 1.45	$ 1.92	$ 2.78	$ 3.72
Diluted	$ 1.45	$ 1.92	$ 2.78	$ 3.72