Stock-Based Compensation - Restricted Common Stock (Details) $ / shares in Units, $ in Thousands		1 Months Ended				12 Months Ended
	Jun. 21, 2018 USD ($)	Oct. 31, 2018 $ / shares	May 31, 2017 USD ($) item $ / shares shares	Apr. 30, 2017 USD ($) $ / shares shares	Jan. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) shares
Executive officer
Weighted Average Grant Date Fair Value
Restricted stock exercise price | $ / shares				$ 0.18
Principal balance of promissory note repaid | $	$ 200
Interest on promissory note repaid | $	100
Restricted Common Stock
Number of shares
Unvested restricted common stock beginning of period						1,559,401
Vested						(1,258,837)
Forfeited						(201,250)
Unvested restricted common stock end of period						99,314	1,559,401
Weighted Average Grant Date Fair Value
Outstanding at the ending (in dollars per share) | $ / shares						$ 0.502
Weighted Average Grant Date Fair Value- vested (in dollars per share) | $ / shares						0.519
Weighted Average Grant Date Fair Value- Forfeited (in dollars per share) | $ / shares						0.387
Ending at the beginning (in dollars per share) | $ / shares						$ 0.526	$ 0.502
Number of shares exercised								1,400,000
Repurchase of unvested restricted common stock (in shares)						466,667
Amount recorded in balance sheet due to promissory notes received from sale of common stock | $			$ 0	$ 0	$ 0
Principal amount of promissory note forgiven | $	2,500
Unvested restricted common stock							670,834
The aggregate intrinsic value of restricted stock awards vested | $						$ 16,300	$ 34,000	$ 900
Incremental share based compensation expense | $							$ 1,500
Restricted Common Stock | Executive officer
Number of shares
Unvested restricted common stock beginning of period			460,000
Unvested restricted common stock end of period				460,000
Weighted Average Grant Date Fair Value
Restricted common stock exercise price | $ / shares				$ 0.19
Principal amount of promissory note received in exchange for restricted common stock | $				$ 100
Principal balance of promissory note repaid | $	100
Interest on promissory note repaid | $	100
Interest on promissory note forgiven | $	$ 100
Restricted Common Stock | Board of Directors Chairman
Number of shares
Unvested restricted common stock end of period			1,100,000		3,667,014
Weighted Average Grant Date Fair Value
Restricted common stock exercise price | $ / shares			$ 1.65		$ 0.19
Principal amount of promissory note received in exchange for restricted common stock | $			$ 2,500
Number of promissory notes | item			2
Market-Based Stock Options
Weighted Average Grant Date Fair Value
Weighted average grant-date fair value (per share) | $ / shares							$ 11.88
Market-Based Stock Options | Vesting based on service period | Executive officer
Weighted Average Grant Date Fair Value
Restricted stock exercise price | $ / shares		$ 16.43
Restricted Stock Units
Number of shares
Issued						277,200
Vested						0
Forfeited						0
Unvested restricted common stock end of period						277,200
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value- issued (in dollars per share) | $ / shares						$ 10.660
Ending at the beginning (in dollars per share) | $ / shares						$ 10.660
Vesting period						3 years