Earnings Per Share (Computation of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Numerator (basic and diluted):
Net income	$ 300,438	$ 321,152
Denominator:
Denominator for basic earnings per share - weighted-average shares	75,022	78,484
Effect of stock options	641	813
Denominator for diluted earnings per share - weighted-average shares and assumed conversion	75,663	79,297
Earnings per share - basic	$ 4.00	$ 4.09
Earnings per share - assuming dilution	$ 3.97	$ 4.05
Antidilutive stock options	349	176
Weighted-average exercise price per share of antidilutive stock options	$ 377.41	$ 347.98

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Numerator Basic and Diluted [Abstract]

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The weighted average exercise price, as of the balance sheet date, of antidilutive stock options awarded under the stock option plan that were not included in the computation of earnings per share.

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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