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Stock-Based Compensation (Details 3) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense $ 16,654 $ 12,362 $ 9,450
Employee Stock Option [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense $ 7,100 $ 5,900 $ 4,700
Restricted Stock Service Based [Member]      
Summary of non-vested stock options      
Non-vested Shares, Beginning Balance (in shares) 1,039    
Shares Granted (in shares) 531    
Shares Vested (in shares) (429)    
Shares Forfeited (in shares) (37)    
Non-vested Shares, Ending Balance (in shares) 1,104 1,039  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]      
Weighted average fair value, Beginning Balance (usd per share) $ 18.23    
Weighted average fair value, Granted (usd per share) 26.25    
Weighted average fair value, Vested (usd per share) 16.54    
Weighted average fair value, Forfeited (usd per share) 22.94    
Weighted average fair value, Ending Balance (usd per share) $ 22.59 $ 18.23  
Restricted Stock Units Service Based [Member]      
Summary of non-vested stock options      
Non-vested Shares, Beginning Balance (in shares) 82    
Shares Granted (in shares) 113    
Shares Vested (in shares) (124)    
Shares Forfeited (in shares) (6)    
Non-vested Shares, Ending Balance (in shares) 65 82  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]      
Weighted average fair value, Beginning Balance (usd per share) $ 21.32    
Weighted average fair value, Granted (usd per share) 23.77    
Weighted average fair value, Vested (usd per share) 22.38    
Weighted average fair value, Forfeited (usd per share) 23.45    
Weighted average fair value, Ending Balance (usd per share) $ 23.36 $ 21.32