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Stock-Based Compensation (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Additional disclosures [Abstract]      
Stock-based compensation expense $ 3,936 $ 3,644 $ 4,378
Number of shares available for future grant (in shares) 1,183,984    
Stock Options [Member]      
Share-based compensation [Abstract]      
Stock awards termination period 10 years    
Stock options [Roll Forward]      
Outstanding, beginning of period (in shares) 112,030    
Exercised (in shares) (44,105)    
Expired (in shares) (1,025)    
Outstanding, end of period (in shares) 66,900 112,030  
Exercisable, end of period (in shares) 65,400    
Expected to vest (in shares) 1,500    
Stock options, weighted average exercise price [Abstract]      
Outstanding, beginning of period (in dollars per share) $ 22.88    
Exercised (in dollars per share) 22.65    
Expired (in dollars per share) 20.36    
Outstanding, end of period (in dollars per share) 23.07 $ 22.88  
Exercisable, end of period (in dollars per share) 22.66    
Expected to vest (in dollars per share) $ 40.63    
Additional disclosures [Abstract]      
Weighted average remaining contractual term, outstanding, end of period 1 year 9 months 11 days    
Weighted average remaining contractual term, exercisable, end of period 1 year 7 months 20 days    
Weighted average remaining contractual term, expected to vest 8 years 1 month 13 days    
Aggregate intrinsic value, outstanding, end of period $ 779,933    
Aggregate intrinsic value, exercisable, end of period 779,933    
Aggregate intrinsic value, expected to vest 0    
Stock-based compensation expense 11 $ 18 235
Proceeds from stock options exercised 999 3,083 8,398
Tax benefits related to stock options exercised 173 650 1,223
Intrinsic value of stock options exercised 692 1,699 3,143
Fair value of shares vested during the year 16 329 105
Restricted Stock [Member]      
Additional disclosures [Abstract]      
Stock-based compensation expense $ 3,900 $ 3,500 4,200
Restricted Stock [Member] | Employees [Member]      
Share-based compensation [Abstract]      
Stock awards vesting period 5 years    
Restricted Stock [Member] | Non-employee Directors [Member]      
Share-based compensation [Abstract]      
Stock awards vesting period 3 years    
Restricted Stock Units (RSUs) [Member]      
Restricted stock and restricted stock units [Roll Forward]      
Unvested, beginning of period (in shares) 534,738    
Forfeited (in shares) (5,999)    
Vested (in shares) (123,642)    
Granted (in shares) 140,957    
Unvested, end of period (in shares) 546,054 534,738  
Restricted stock and restricted stock units, weighted average grant date fair value [Abstract]      
Unvested, beginning of period (in dollars per share) $ 25.77    
Forfeited (in dollars per share) 29.56    
Vested (in dollars per share) 23.44    
Granted (in dollars per share) 33.80    
Unvested, end of period (in dollars per share) $ 28.39 $ 25.77  
Restricted Stock Awards and Stock Units [Member]      
Additional disclosures [Abstract]      
Tax benefit on restricted stock awards $ 1,200 $ 2,500 $ 2,900
Unrecognized compensation cost $ 5,400    
Unrecognized compensation cost, weighted average period of recognition 2 years