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		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Net Income (Loss) Available to Common Stockholders, Basic [Abstract]
Net income (numerator for basic and diluted calculations)	$ 157,996	$ 137,955	$ 492,956	$ 273,878
Shares:
Weighted average outstanding shares (denominator for basic calculation)	68,643	70,865	69,426	72,342
Equivalent shares from outstanding stock options	692	526	675	498
Denominator for diluted calculation	69,335	71,391	70,101	72,840
Earnings Per Share:
Basic earnings per share	$ 2.30	$ 1.95	$ 7.10	$ 3.79
Diluted earnings per share	$ 2.28	$ 1.93	$ 7.03	$ 3.76