Stockholders' Equity Common Stock - Employee Stock Purchase Plan - Additional Information (Detail) - Employee Stock Purchase Plan [Member]	9 Months Ended
Sep. 30, 2018 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of eligible earning contributed toward semi-annual purchase of common stock	15.00%
Offering period under the plan	6 months
Percentage of purchase price with respect to each offering period	85.00%
Risk-free interest rate	2.30%
Expected term (in years)	6 months
Expected volatility	60.20%
Expected dividend yield	0.00%
Aggregate shares of common stock reserved for issuance	1,600,000
Shares issued under ESPP	400,000
Percentage of common stock shares outstanding	1.00%

Offering period under the plan.

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Percentage common stock outstanding shares.

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- Definition

Percentage of purchase price with respect to each offering period.

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- Definition

Number of common shares reserved for future issuance related to deferred compensation arrangements with individuals.

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- Definition

Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

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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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The 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.

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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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Number of shares issued during the period as a result of an employee stock purchase plan.

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