XML 107 R91.htm IDEA: XBRL DOCUMENT v3.20.4
Stock-Based Compensation - Assumptions Used to Determine Grant Date Fair Value of Equity and Liability Component (Details) - TSR Performance Share Awards - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Stockholders' Equity      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Fair value per performance share award granted during the period $ 13.79 $ 20.63 $ 19.92
Stock price volatility 29.50% 31.30% 37.30%
Risk free rate of return 1.40% 2.50% 2.40%
Liability      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock price volatility, minimum rate 42.40% 29.80% 29.90%
Stock price volatility, maximum rate 52.40% 30.40% 31.10%
Risk free rate of return 10.00% 160.00%  
Risk free rate of return, minimum rate     2.50%
Risk free rate of return, maximum rate     2.60%
Minimum | Liability      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Fair value per performance share award granted during the period $ 10.37 $ 6.18 $ 15.15
Maximum | Liability      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Fair value per performance share award granted during the period $ 10.81 $ 14.80 $ 20.12