Earnings Per Share (Computation of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator (basic and diluted):
Net income	$ 531,667	$ 353,681	$ 832,105	$ 674,833	[1]
Denominator:
Denominator for basic earnings per share - weighted-average shares	74,205	77,613	74,611	78,047
Effect of stock options	628	799	635	807
Denominator for diluted earnings per share - weighted-average shares and assumed conversion	74,833	78,412	75,246	78,854
Earnings per share - basic	$ 7.16	$ 4.56	$ 11.15	$ 8.65
Earnings per share - assuming dilution	$ 7.10	$ 4.51	$ 11.06	$ 8.56
Antidilutive stock options	341	184	348	188
Weighted-average exercise price per share of antidilutive stock options	$ 378.84	$ 357.18	$ 378.29	$ 357.33

[1] Note: Certain prior period amounts have been reclassified to conform to current period presentation.