Earnings Per Share (Reconciliation of the Numerators and Denominators of the Basic and Diluted Per Shares) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Earnings:
Net income (numerator for basic and diluted calculations)	$ 198,296	$ (49,612)	$ 334,960	$ 135,923
Shares:
Weighted average outstanding shares (denominator for basic calculation)	69,076	72,350	69,823	73,089
Equivalent shares from outstanding stock options	642	0	666	484
Denominator for diluted calculation	69,718	72,350	70,489	73,573
Earnings Per Share:
Basic earnings per share	$ 2.87	$ (0.69)	$ 4.80	$ 1.86
Diluted earnings per share	$ 2.84	$ (0.69)	$ 4.75	$ 1.85