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
	Mar. 31, 2016	Mar. 31, 2015
Net Income (Loss) Available to Common Stockholders, Basic [Abstract]
Net income (numerator for basic and diluted calculations)	$ 76,472	$ 125,114
Shares:
Weighted average outstanding shares (denominator for basic calculation)	64,568	68,141
Equivalent shares from outstanding stock options	649	801
Denominator for diluted calculation	65,217	68,942
Earnings Per Share:
Basic earnings per share	$ 1.18	$ 1.84
Diluted earnings per share	$ 1.17	$ 1.81