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Stock-Based Compensation - Restricted and Performance Stock Units Rollforward (Details) - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Restricted Stock Units      
Shares      
Nonvested at the beginning of the period (in shares) 153,442    
Granted (in shares) 0 37,235  
Vested (in shares) (102,166)    
Nonvested at the end of the period (in shares) 51,276 153,442  
Weighted Average Grant-Date Fair Value      
Nonvested at the beginning of the period (in dollars per share) $ 27.46    
Vested (in dollars per share) 24.56    
Nonvested at the end of the period (in dollars per share) $ 33.24 $ 27.46  
Performance Shares      
Shares      
Nonvested at the beginning of the period (in shares) 212,096    
Granted (in shares) 96,056 125,232 100,715
Vested (in shares) (81,115)    
Forfeited (in shares) (23,173)    
Expired (in shares) (3,646)    
Nonvested at the end of the period (in shares) 200,218 212,096  
Weighted Average Grant-Date Fair Value      
Nonvested at the beginning of the period (in dollars per share) $ 35.01    
Granted (in dollars per share) 37.89    
Vested (in dollars per share) 30.01    
Forfeited (in dollars per share) 36.27    
Expired (in dollars per share) 37.59    
Nonvested at the end of the period (in dollars per share) $ 35.27 $ 35.01