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Stock-Based Compensation, Restricted Stock (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Employee service share-based compensation, aggregate disclosures [Abstract]      
Share based compensation costs $ 6,200 $ 8,100 $ 6,300
Restricted Stock [Member]      
Employee service share-based compensation, aggregate disclosures [Abstract]      
Unrecognized stock-based compensation expense $ 5,100    
Weighted average period over which unrecognized stock-based compensation expense is expected to be recognized 3 years    
Share based compensation costs $ 4,400 5,900 5,800
Reversals of compensation expense related to restricted stock forfeitures $ 2,400 $ 2,400 $ 3,800
Restricted Stock [Roll Forward]      
Balance, beginning of year (in shares) 180,110 227,213 284,245
Granted (in shares) 69,361 69,539 155,165
Vested (in shares) (59,649) (61,274) (88,746)
Canceled (in shares) (55,244) (55,368) (123,451)
Balance, end of year (in shares) 134,578 180,110 227,213
Weighted Average Grant Date Fair Value [Abstract]      
Balance, beginning of year (in dollars per share) $ 58.57 $ 49.57 $ 58.63
Granted (in dollars per share) 76.26 78.00 38.37
Vested (in dollars per share) 56.44 52.51 57.38
Canceled (in dollars per share) 58.57 52.74 50.72
Balance, end of year (in dollars per share) $ 68.64 $ 58.57 $ 49.57