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Stockholder's Equity Valuation Assumptions (Details) - Stock options
6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk-free interest rate 1.93% 2.81%
Expected volatility 36.95% 36.60%
Expected life 4 years 3 months 8 days 4 years 3 months 14 days
Dividend yield 0.00% 0.00%