Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation - Performance-Based Awards (Details)

v3.19.1
Stock-Based Compensation - Performance-Based Awards (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Performance Cash Units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Nonvested weighted average nominal value per share (in dollars per share) $ 100.0    
Percentage of number of shares earned related to performance maximum 200.00%    
Performance period 3 years    
Maximum percent of units granted at maximum achievement level 250.00%    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Nonvested, Beginning Balance (in shares) 23,021    
Granted (in shares) 16,149 14,153 17,091
Vested (in shares) (10,771)    
Forfeited (in shares) (791)    
Nonvested, Ending Balance (in shares) 27,608 23,021  
Stock-based compensation expense, RSUs $ 0.2 $ 1.0 $ 2.3
Performance-based Phantom Stock Units      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Nonvested, Beginning Balance (in shares) 87,395    
Granted (in shares) 107,645 44,020 77,652
Vested (in shares) (48,937)    
Forfeited (in shares) (3,778)    
Nonvested, Ending Balance (in shares) 142,325 87,395  
Stock-based compensation expense, RSUs $ (0.6) $ (0.9) $ 1.3