Earnings Per Share (Reconciliation of Numerators and Denominators of Basic and Diluted Per-Share Computations) (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Calculation Of Numerator And Denominator In Earnings Per Share [Line Items]
Net income - basic and diluted numerator:	$ 178,186	$ 256,854	$ 564,816	$ 774,052
Weighted average shares - basic (denominator):	139,030	139,027	139,029	139,027
Effect of dilutive potential shares Stock options and stock appreciation rights	23	14	17	21
Total weighted-average shares outstanding	139,053	139,041	139,046	139,048
Earnings per share:
Basic	$ 1.28	$ 1.85	$ 4.06	$ 5.57
Diluted	$ 1.28	$ 1.85	$ 4.06	$ 5.57