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Stockholders' Equity (Schedule of Fair Value of Employee Stock Options) (Details) - Stock Options [Member]
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expected term in years 5 years 2 months 12 days 5 years 2 months 12 days
Expected volatility 65.00% 67.00%
Risk-free interest rate 2.80% 2.50%
Dividend yield