Share-Based Compensation (Summary of Stock Option Activity) (Details) - $ / shares	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of shares
Beginning balance (in shares)	1,676,778	2,004,598	2,560,571
Granted (in shares)	320,913	256,818	194,001
Exercised (in shares)	(285,954)	(569,808)	(729,346)
Expired (in shares)	(22,685)	(4,330)	(2,000)
Forfeited (in shares)	(5,395)	(10,500)	(18,628)
Ending balance (in shares)	1,683,657	1,676,778	2,004,598
Weighted average exercise price
Beginning balance (in dollars per share)	$ 34.77	$ 29.85	$ 27.06
Granted (in dollars per share)	45.61	50.80	55.13
Exercised (in dollars per share)	26.48	24.61	26.79
Expired (in dollars per share)	30.17	22.37	25.74
Forfeited (in dollars per share)	51.34	43.13	31.11
Ending balance (in dollars per share)	$ 38.26	$ 34.77	$ 29.85
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Number of shares, Outstanding stock options exercisable (in shares)	1,137,596	1,239,821	1,448,244
Weighted average exercise price, Outstanding stock options exercisable (in dollars per share)	$ 33.42	$ 28.95	$ 26.68

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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Net number of share options (or share units) granted during the period.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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