Employee Stock Options (Details) - Employee Stock Option [Member]	3 Months Ended	12 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Summary of assumptions used to estimate fair value of stock options granted
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Expected volatility	90.00%
Risk-free interest rate		2.49%
Expected life of options	4 years		4 years
Minimum [Member]
Summary of assumptions used to estimate fair value of stock options granted
Expected volatility		83.00%	80.00%	82.00%
Risk-free interest rate	2.40%		2.41%	1.50%
Expected life of options		2 years 6 months		2 years 6 months
Maximum [Member]
Summary of assumptions used to estimate fair value of stock options granted
Expected volatility		86.00%	96.00%	101.00%
Risk-free interest rate	2.47%		2.93%	2.62%
Expected life of options		3 years		4 years

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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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- Definition

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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

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