Net Loss Per Share - Computation of Basic and Diluted Net Loss Per Share for Continuing and Discontinued Operations (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Loss from continuing operations	$ (9,313)	$ (3,076)	$ (18,231)	$ (11,129)
Loss from discontinued operations	(42)	(61)	(116)	(220)
Net loss	$ (9,355)	$ (3,137)	$ (18,347)	$ (11,349)
Denominator:
Weighted average common shares outstanding	42,497	13,954	32,658	11,400
Weighted average unvested common shares subject to repurchase		(16)		(51)
Weighted average common shares outstanding—basic and diluted	42,497	13,938	32,658	11,349
Net loss per share, basic and diluted:
Continuing operations, net loss per share, basic and diluted	$ (0.22)	$ (0.22)	$ (0.56)	$ (0.98)
Discontinued operations, net loss per share, basic and diluted	0.00	(0.01)	0.00	(0.02)
Net loss per share, basic and diluted	$ (0.22)	$ (0.23)	$ (0.56)	$ (1.00)

The amount of net income or loss for the period per each share in instances when basic and diluted earnings per share are the same amount and reported as a single line item on the face of the financial statements. Basic earnings per share is the amount of net income or loss for the period per each share of common stock or unit outstanding during the reporting period. Diluted earnings per share includes the amount of net income or loss for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Amount after tax of income (loss) from continuing operations attributable to the parent.

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The amount of net income (loss) from continuing operations per each basic and diluted share of common stock or unit when the per share amount is the same for both basic and diluted shares.

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Amount after tax of income (loss) from a discontinued operation attributable to the parent. Includes, but is not limited to, the income (loss) from operations during the phase-out period, gain (loss) on disposal, gain (loss) for reversal of write-down (write-down) to fair value, less cost to sell, and adjustments to a prior period gain (loss) on disposal.

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Per basic and diluted share amount, after tax, of income (loss) from the day-to-day business activities of the discontinued operation and gain (loss) from the disposal of the discontinued operation, when the per share amount is the same.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Average number of shares or units issued and outstanding that are used in calculating basic and diluted earnings per share (EPS).

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Number of shares of common stock subject to repurchase or cancellation determined by relating the portion of time within a reporting period that these shares have been outstanding to the total time in that period. Common stock subject to repurchase are outstanding common shares that are contingently returnable (that is, subject to recall).

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This element represents the weighted average total number of shares issued throughout the period including the first (beginning balance outstanding) and last (ending balance outstanding) day of the period before considering any reductions (for instance, shares held in treasury) to arrive at the weighted average number of shares outstanding. Weighted average relates to the portion of time within a reporting period that common shares have been issued and outstanding to the total time in that period. Such concept is used in determining the weighted average number of shares outstanding for purposes of calculating earnings per share (basic).

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