Stock-Based Compensation (Assumptions Used in Estimation of Fair Value of Stock) (Details) - $ / shares	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average Black-Scholes fair value of stock options granted	$ 1.33	$ 0.81	$ 1.38	$ 1.03
Risk-free interest rate, minimum	2.59%	1.63%	2.26%	1.63%
Risk-free interest rate, maximum	2.74%	1.71%	2.74%	2.34%
Dividend yield	0.00%	0.00%	0.00%	0.00%
Volatility, minimum	113.68%	106.92%	113.68%	88.91%
Volatility, maximum	114.24%	111.46%	114.24%	111.46%
Expected forfeiture rate	0.00%	0.00%	0.00%	0.00%
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, minimum	0.74%	0.57%	0.66%	0.45%
Risk-free interest rate, maximum	1.79%	0.70%	1.79%	0.70%
Dividend yield	0.00%	0.00%	0.00%	0.00%
Volatility, minimum	59.84%	54.67%	59.84%	45.98%
Volatility, maximum	203.83%	267.85%	203.83%	267.85%
Expected forfeiture rate	0.00%	0.00%	0.00%	0.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	4 years 1 month 6 days	4 years 2 months 5 days	4 years 1 month 6 days	4 years 2 months 5 days
Minimum [Member] \| Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average Black-Scholes fair value of stock options granted	$ 0.66	$ 1.05	$ 0.45	$ 1.05
Expected term (in years)	6 months	6 months	6 months	6 months
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	4 years 1 month 10 days	4 years 7 months 6 days	4 years 1 month 20 days	7 years 5 months 16 days
Maximum [Member] \| Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average Black-Scholes fair value of stock options granted	$ 3.53	$ 5.47	$ 3.53	$ 5.47
Expected term (in years)	2 years	2 years	2 years	2 years

Estimated rate of forfeitures.

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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 maximum 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.

+ References

No definition available.

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The estimated measure of the minimum 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.

+ References

No definition available.

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- Definition

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

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No definition available.

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- Definition

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

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

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