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Stock-Based Compensation - Stock Option Activity (Details) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Number of Stock Options    
Outstanding, beginning of period (in shares) 327,270  
Exercised (in shares) (8,500)  
Outstanding, end of period (in shares) 318,770 327,270
Exercisable (in shares) 296,738  
Weighted Average Exercise Price    
Outstanding, beginning of period (in USD per share) $ 20.21  
Exercised (in USD per share) 18.51  
Outstanding, end of period (in USD per share) 20.25 $ 20.21
Exercisable (in USD per share) $ 19.67  
Weighted Average Remaining Contractual Life (years)    
Outstanding 4 years 25 days 4 years 2 months 42 days
Exercisable 3 years 7 months 50 days  
Aggregate Intrinsic Value    
Outstanding, beginning of period $ 2,255  
Exercised 86  
Outstanding, end of period 1,638 $ 2,255
Exercisable $ 1,638