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Stock-Based Compensation (Details) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]        
Outstanding at beginning of period (in shares) 873,849 1,040,569    
Granted (in shares) 206,695 243,940    
Converted (in shares) (96,616) (173,210)    
Expired (in shares) 0 0    
Forfeited (in shares) 0 (3,800)    
Outstanding at end of period (in shares) 983,928 1,107,499 1,040,569  
Vested (in shares) 326,928 324,599    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]        
Outstanding at beginning of period, Weighted average grant-date fair value (in dollars per share) $ 12.30 $ 9.97    
Granted, Weighted average grant-date fair value (in dollars per share) 26.53 17.52    
Converted, Weighted average grant-date fair value (in dollars per share) 10.89 9.69    
Expired, Weighted average grant-date fair value (in dollars per share) 0.00 0.00    
Forfeited, Weighted average grant-date fair value (in dollars per share) 0.00 13.66    
Outstanding at end of period, Weighted average grant-date fair value (in dollars per share) 15.43 11.66 $ 9.97  
Vested (in dollars per share) $ 7.18 $ 6.39    
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]        
Share-based compensation expense $ 1.0 $ 0.8    
Unrecognized share-based compensation expense $ 8.5      
Unrecognized share-based compensation, weighted average recognition period 1 year 10 months      
Restricted Stock [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Requisite service period 3 years      
Stock Units [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Requisite service period 3 years      
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]        
Historical volatility period 3 years   3 years 3 years
Risk-free interest rate 2.40%      
Expected volatility rate 33.80%      
Market Condition Award [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]        
Granted, Weighted average grant-date fair value (in dollars per share) $ 31.60      
Performance Condition Award [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]        
Granted, Weighted average grant-date fair value (in dollars per share) $ 25.15      
Time-Based Awards [Member] | Maximum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]        
Number of additional outstanding shares issued (in shares) 1,219,878      
Director [Member] | Time-Based Awards [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]        
Vested (in shares) 326,928      
Director [Member] | Time-Based Awards [Member] | Minimum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Requisite service period 6 months      
Director [Member] | Time-Based Awards [Member] | Maximum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Requisite service period 12 months