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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Net Income (Loss) Available to Common Stockholders, Basic [Abstract]
Net income (numerator for basic and diluted calculations)	$ 262,765	$ 301,199	$ 634,970	$ 605,803
Shares:
Weighted average outstanding shares (denominator for basic calculation)	62,666	63,279	62,701	63,941
Equivalent shares from outstanding stock options	1,123	1,017	1,218	1,189
Denominator for diluted calculation	63,789	64,296	63,919	65,130
Earnings Per Share:
Basic earnings per share	$ 4.19	$ 4.76	$ 10.13	$ 9.47
Diluted earnings per share	$ 4.12	$ 4.68	$ 9.93	$ 9.30