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Stockholders' Equity Performance Awards Assumptions (Details) - $ / shares
3 Months Ended
Feb. 20, 2019
Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk-free interest rate   2.42%
Performance Shares [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected holding period (years) 4 years 10 months 10 days  
Share price at grant date $ 19.92  
Expected volatility 25.70%  
Risk-free interest rate 2.47%