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Stock-Based Compensation and Directors Stock Purchase Plan Stock-Based Compensation and Directors Stock Purchase Plan (Additional Information About Stock Options and SARs Exercises) (Details) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
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Share-based Payment Arrangement, Noncash Expense [Abstract] |  |  |
Intrinsic value of options and SARs exercised | $ 6,278 | $ 7,109 | $ 9,632
Tax benefit realized from options and SARs exercised | $ 1,252 | $ 1,385 | $ 1,928

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