Earnings Per Share (Computation of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator (basic and diluted):
Net income	$ 527,252	$ 391,293	$ 1,359,357	$ 1,066,126
Denominator:
Denominator for basic earnings per share - weighted-average shares	73,916	76,172	74,377	77,415
Effect of stock options	670	797	649	805
Denominator for diluted earnings per share - weighted-average shares and assumed conversion	74,586	76,969	75,026	78,220
Earnings per share - basic	$ 7.13	$ 5.14	$ 18.28	$ 13.77
Earnings per share - assuming dilution	$ 7.07	$ 5.08	$ 18.12	$ 13.63
Antidilutive stock options	153	207	327	214
Weighted-average exercise price per share of antidilutive stock options	$ 409.07	$ 360.80	$ 384.43	$ 360.36