Stock-Based Awards - Schedule of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Shares Issuable Under Options
Shares Issuable Under Options, Beginning balance	5,230,831
Shares Issuable Under Options, Granted	3,985,025
Shares Issuable Under Options, Exercised	(28,583)
Shares Issuable Under Options, Forfeited	(1,266,856)
Shares Issuable Under Options, Ending balance	7,920,417	5,230,831
Shares Issuable Under Options, Vested and expected to vest	7,065,332
Shares Issuable Under Options, Exercisable	3,790,742
Weighted Average Exercise Price
Weighted Average Exercise Price, Beginning balance	$ 8.67
Weighted Average Exercise Price, Granted	4.06
Weighted Average Exercise Price, Exercised	2.72
Weighted Average Exercise Price, Forfeited	6.84
Weighted Average Exercise Price, Ending balance	6.67	$ 8.67
Weighted Average Exercise Price, Vested and expected to vest	6.96
Weighted Average Exercise Price, Exercisable	$ 8.67
Weighted Average Remaining Contractual Term	7 years 7 months 6 days	7 years 6 months
Weighted Average Remaining Contractual Term, Vested and Expected to vest	7 years 3 months 18 days
Weighted Average Remaining Contractual Term, Exercisable	6 years
Other disclosures
Aggregate Intrinsic Value	$ 704	$ 654
Aggregate Intrinsic Value, Exercisable	651
Aggregate intrinsic value of stock options exercised	$ 54	$ 551	$ 408
Weighted average fair value of stock option granted	$ 2.99	$ 4.48	$ 6.44

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

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