Earnings Per Share (Reconciliation of the Numerators and Denominators of the Basic and Diluted Per Shares) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Net Income (Loss) Available to Common Stockholders, Basic [Abstract]
Net income (numerator for basic and diluted calculations)	$ 83,534	$ 157,996	$ 339,039	$ 492,956
Shares:
Weighted average outstanding shares (denominator for basic calculation)	66,205	68,643	66,895	69,426
Equivalent shares from outstanding stock options	677	692	749	675
Denominator for diluted calculation	66,882	69,335	67,644	70,101
Earnings Per Share:
Basic earnings per share	$ 1.26	$ 2.30	$ 5.07	$ 7.10
Diluted earnings per share	$ 1.25	$ 2.28	$ 5.01	$ 7.03