Stockholders' Equity - Assumptions Used to Determine Estimated Fair Value of Stock Options Granted (Details) - $ / shares |
12 Months Ended | |
---|---|---|
Dec. 31, 2017 |
Dec. 31, 2015 |
|
Assumptions used to determine the fair value of stock options [Abstract] | ||
Weighted average grant date fair value (in dollars per share) | $ 84 | |
Stock Options [Member] | ||
Assumptions used to determine the fair value of stock options [Abstract] | ||
Weighted average risk-free interest rates (in hundredths) | 2.15% | 1.82% |
Weighted average expected volatility (in hundredths) | 170.42% | 97.70% |
Weighted average expected option term (in years) | 7 years 3 months 14 days | 5 years 1 month 24 days |
Weighted average grant date fair value (in dollars per share) | $ 82.34 | $ 4,964.73 |