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Stock Plans (Schedule of Restricted and Restricted Stock Units Activity) (Details) - Restricted Stock Units (RSUs) [Member] - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Number of Shares      
Balance at beginning of year (in shares) 1,909,642    
Granted (in shares) 1,162,118    
Vested (in shares) (542,331)    
Forfeited (in shares) (290,050)    
Balance at end of year, (in shares) 2,239,379 1,909,642  
Weighted-Average Grant Date Fair Value Per Share      
Balance at beginning of year (USD per share) $ 61.46    
Granted (USD per share) 42.59 $ 52.03 $ 67.17
Vested (USD per share) 66.22    
Forfeited (USD per share) 51.91    
Balance at end of year (USD per share) $ 51.76 $ 61.46