Quarterly report pursuant to Section 13 or 15(d)

Equity and Share-Based Compensation - Chief Executive Officer Restricted Stock Units Containing a Market Condition (Details)

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Equity and Share-Based Compensation - Chief Executive Officer Restricted Stock Units Containing a Market Condition (Details) - Performance stock units - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Mar. 01, 2018
Nov. 01, 2017
Sep. 30, 2018
Sep. 30, 2018
Chief Executive Officer        
Share-Based Compensation        
Granted (in shares)   135,778    
RSUs granted based on actual TSR (as a percentage)   50.00%    
RSUs granted based on relative TSR (as a percentage)   50.00%    
Days considered for calculation of average stock price   20 days    
Assumptions used to estimate fair value of restricted stock unit awards with market condition        
Service period (in years)   3 years    
Share-based compensation costs recognized     $ 0.1 $ 0.3
Unrecognized expense for share-based compensation     1.0 $ 1.0
Weighted-average period for over which unrecognized expense will be recognized       2 years 1 month 6 days
Chief Executive Officer | Maximum        
Share-Based Compensation        
Percentage of vesting of RSUs granted (as a percentage)   120.00%    
Executive officer        
Share-Based Compensation        
Granted (in shares) 96,305      
Assumptions used to estimate fair value of restricted stock unit awards with market condition        
Service period (in years)       3 years
Share-based compensation costs recognized     0.1 $ 0.3
Unrecognized expense for share-based compensation     $ 1.0 $ 1.0
Weighted-average period for over which unrecognized expense will be recognized       2 years 3 months 18 days