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Stock-Based Compensation - Restricted and Performance Unit Activity (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]      
Allocated share-based compensation expense $ 3,700 $ 3,200 $ 3,000
Total compensation cost not yet recognized $ 13,300    
Retricted and performance unit activity      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Outstanding - beginning of the period (in shares) 379,419    
Granted (in shares) 277,725    
Vested (in shares) (152,887)    
Forfeited (in shares) (25,366)    
Outstanding - end of the period (in shares) 478,891 379,419  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]      
Outstanding - beginning of the period, weighted-average grant date fair value (in dollars per share) $ 16.50    
Granted, weighted-average grant date fair value (in dollars per share) 16.25    
Vested, weighted-average grant date fair value (in dollars per share) 16.48    
Forfeited, weighted-average grant date fair value (in dollars per share) 16.43    
Outstanding - end of the period, weighted-average grant date fair value (in dollars per share) $ 16.37 $ 16.50  
Restricted And Performance Unit Activity [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]      
Equity instruments other than options, vested in period $ 2,700 $ 2,700 $ 1,900
Stock options      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]      
Total compensation cost not yet recognized, period for recognition 2 years 6 months    
Employee Stock Purchase Plan (ESPP) [Domain]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Offering Date 10.00%    
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Employee Subscription Rate 20.00%    
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Number of Shares Per Employee, Value $ 25    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]      
Employee Stock Ownership Plan (ESOP), Compensation Expense $ 165