Basis of Presentation and Significant Accounting Policies - Weighted Average Assumptions (Details)	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Stock-based Compensation, Valuation Assumptions
Risk-free interest rate, minimum	2.73%	2.01%	2.49%	2.01%
Risk-free interest rate, maximum	2.77%	2.07%	2.77%	2.07%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Expected volatility	54.60%	59.80%
Expected volatility, minimum			54.60%	59.80%
Expected volatility, maximum			55.10%	61.00%
Minimum
Stock-based Compensation, Valuation Assumptions
Expected term	6 years 2 months 16 days	6 years 1 month 13 days	6 years 2 months 5 days	6 years 29 days
Maximum
Stock-based Compensation, Valuation Assumptions
Expected term	6 years 8 months 9 days	6 years 7 months 13 days	6 years 8 months 9 days	6 years 7 months 13 days

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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- 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.

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No definition available.

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- Definition

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.

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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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No definition available.

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- Definition

Weighted average expected volatility rate of share-based compensation awards.

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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
-Subparagraph (f)(2)(i)
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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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