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Equity Compensation (Additional Information) (Details)
3 Months Ended 9 Months Ended 12 Months Ended 63 Months Ended
Sep. 30, 2018
USD ($)
Sep. 30, 2017
USD ($)
Sep. 30, 2018
USD ($)
offering_periods
shares
Sep. 30, 2017
USD ($)
Dec. 31, 2017
Jun. 30, 2017
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Proceeds from the exercise of stock options, net     $ 734,000 $ 1,926,000    
Deferred Stock Units            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Compensation expense (income) $ 0 $ 100,000 $ 900,000 1,000,000    
Stock vested (shares) | shares     9,250      
Employee Stock Option            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock options, contractual term (years)     10 years      
Stock options, grants in period, gross | shares           0
Options exercised, total intrinsic value     $ 700,000      
Proceeds from the exercise of stock options, net     $ 2,200,000      
Performance-Based Restricted Stock            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Restricted stock award program, measurement period (years)     3 years      
Expected dividend yield (percent)     0.00%      
Compensation expense (income) 1,300,000 1,400,000 $ 3,100,000 2,900,000    
Stock vested (shares) | shares     81,230      
Performance-Based Restricted Stock | Minimum            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Restricted stock award program, awarded shares as a percentage of the original award amount (percent)     0.00%      
Performance-Based Restricted Stock | Maximum            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Restricted stock award program, awarded shares as a percentage of the original award amount (percent)     200.00%      
Time Based Restricted Stock            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Compensation expense (income) 1,400,000 $ 1,600,000 $ 4,200,000 $ 4,200,000    
Stock vested (shares) | shares     79,375      
Employee Stock Purchase Plan            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Compensation expense (income) $ 300,000   $ 100,000      
Employee stock purchase plan, number of offering (offering period) | offering_periods     2      
Employee stock purchase plan, offering period (months)     6 months      
Employee stock purchase plan, purchase price discount (percent)         15.00%