Equity Incentive Plans - Schedule of Fair Value Assumptions Used for All Equity Based Awards Estimated Using Black-Scholes Option Pricing Model (Details)	9 Months Ended	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Stock Option Plans
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, minimum	52.00%	57.00%	57.00%
Expected volatility, maximum	55.00%	59.00%	59.00%
Risk-free interest rate, minimum	2.70%	1.97%	1.97%
Risk-free interest rate, maximum	2.89%	2.23%	2.23%
Dividend yield	0.00%	0.00%	0.00%
Stock Option Plans \| Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	5 years 6 months	5 years 6 months	5 years 6 months
Stock Option Plans \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 years 3 months	6 years 3 months	6 years 3 months
ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 months	6 months	6 months
Expected volatility, minimum	45.00%	76.00%	76.00%
Expected volatility, maximum	53.00%	82.00%	82.00%
Risk-free interest rate, minimum	1.61%	0.62%	0.62%
Risk-free interest rate, maximum	2.14%	1.13%	1.13%
Dividend yield	0.00%	0.00%	0.00%

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.

+ Details

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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.

+ References

No definition available.

+ Details

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- Definition

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

+ References

No definition available.

+ Details

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- Definition

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

+ References

No definition available.

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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

No definition available.

+ Details

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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
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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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