Warrants (Details) - Warrant [Member]	3 Months Ended	12 Months Ended
Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Summary of assumptions used to estimate fair value of stock warrants granted
Expected dividend yield	0.00%	0.00%	0.00%
Expected volatility	90.00%	91.00%	80.00%
Risk-free interest rate	2.40%	2.93%	2.62%
Expected life of warrants	4 years	4 years
Minimum [Member]
Summary of assumptions used to estimate fair value of stock warrants granted
Expected life of warrants			4 years
Maximum [Member]
Summary of assumptions used to estimate fair value of stock warrants granted
Expected life of warrants			5 years

No definition available.

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

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- Definition

Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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