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, 2019	Mar. 31, 2018
Net Income (Loss) Available to Common Stockholders, Basic [Abstract]
Net income (numerator for basic and diluted calculations)	$ 169,507	$ 100,230
Shares:
Weighted average outstanding shares (denominator for basic calculation)	62,758	64,490
Equivalent shares from outstanding stock options	1,269	1,382
Denominator for diluted calculation	64,027	65,872
Earnings Per Share:
Basic earnings per share	$ 2.70	$ 1.55
Diluted earnings per share	$ 2.65	$ 1.52