Stock-Based Compensation - Additional Information (Detail) - USD ($)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total compensation cost related to unvested stock options and RSU	$ 35,400,000
Weighted-average period of unvested stock options and RSU	2 years 8 months 4 days
Capitalized stock-based employee compensation expense	$ 0	$ 0	$ 0
Weighted-average estimated fair value per share of options granted	$ 11.39	$ 4.10	$ 3.14
Issuance of common stock under employee stock purchase plan, shares	328,710	253,994	202,711
Stock issued under employee stock purchase plans, average exercise price	$ 4.51	$ 3.22	$ 4.04
Weighted-average estimated fair value of shares purchased under ESPP plan	$ 7.07	$ 2.37	$ 2.27
Restricted Stock Units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total compensation cost related to unvested stock options and RSU	$ 4,100,000
Weighted-average period of unvested stock options and RSU	2 years 2 months 4 days

Employee stock purchase plan rights weighted average estimated fair value.

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- Definition

Stock issued under employee stock purchase plans average exercise price.

+ References

No definition available.

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- Definition

Represents the compensation cost capitalized during the period arising from equity-based compensation arrangements (for example, shares of stock, units, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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- Definition

Unrecognized cost of unvested share-based compensation awards.

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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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

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

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

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