Stockholders' Equity - Summary of Stock Option Activity Under Equity Incentive Plan (Details)	12 Months Ended
Dec. 31, 2018 $ / shares shares
Number of Shares
Beginning Balance (shares) \| shares	7,694,870
Granted (shares) \| shares	2,176,935
Exercised (shares) \| shares	(472,762)
Cancelled (shares) \| shares	(646,366)
Ending Balance (shares) \| shares	8,752,677
Weighted-Average Exercise Price
Beginning Balance ($ per share) \| $ / shares	$ 6.77
Granted ($ per share) \| $ / shares	4.32
Exercised ($ per share) \| $ / shares	3.21
Cancelled ($ per share) \| $ / shares	6.83
Ending Balance ($ per share) \| $ / shares	$ 6.35

For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

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Weighted average price of options that were either forfeited or expired.

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Gross number of share options (or share units) granted during the period.

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Number of options outstanding, including both vested and non-vested options.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Number of share options (or share units) exercised during the current period.

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