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Stock-based Compensation - Fair Value Assumptions And Methodology (Details)
12 Months Ended
Dec. 31, 2018
Fair value assumptions and methodology [Abstract]  
Expected volatility range of stock, minimum (in hundredths) 39.80%
Expected volatility range of stock, maximum (in hundredths) 40.10%
Expected life of option, range in years 5 years
Risk-free interest rate range, minimum (in hundredths) 2.20%
Risk-free interest rate range, maximum (in hundredths) 2.80%
Expected dividend yield on stock (in hundredths) 0.00%