UNAUDITED CONDENSED CONSOLIDATED STATEMENT OF STOCKHOLDERS’ DEFICIT - 6 months ended Jun. 30, 2018 - USD ($) $ in Thousands	Redeemable convertible preferred stock Common Stock	Redeemable convertible preferred stock Additional Paid-in Capital	Redeemable convertible preferred stock	Series A convertible preferred stock Common Stock	Series A convertible preferred stock Additional Paid-in Capital	Series A convertible preferred stock	Common Stock	Treasury Stock	Additional Paid-in Capital	Accumulated Deficit	Total
Beginning balance at Dec. 31, 2017							$ 11	$ (6)	$ 13,429	$ (273,513)	$ (260,079)
Beginning balance (in shares) at Dec. 31, 2017							11,139,690	53,676			11,139,690
Increase (Decrease) in Stockholders' Equity (Deficit)
Accretion of preferred stock to redemption value									(17,550)	(181,942)	$ (199,492)
Conversion of convertible preferred stock upon initial public offering	$ 44	$ 532,652	$ 532,696	$ 2	$ 1,719
Conversion of convertible preferred stock upon initial public offering (in shares)	44,370,560			1,709,063		1,721,000
Issuance of common stock upon initial public offering, net of underwriting discounts and commissions and offering costs incurred of $4858							$ 9		157,697		157,706
Issuance of common stock upon initial public offering, net of underwriting discounts and commissions and offering costs incurred (in shares)							9,200,000
Issuance of common stock upon exercise of common stock warrants							$ 1		11,603		11,604
Issuance of common stock upon exercise of common stock warrants (in shares)							712,063
Repurchase of common stock (in shares)							(1,728)	1,728
Exercise of stock options						$ 211	$ 1		2,519		2,520
Exercise of stock options (in shares)						360,385	624,019
Stock-based compensation expense									5,876		5,876
Net loss										(45,875)	(45,875)
Ending balance at Jun. 30, 2018							$ 68	$ (6)	$ 707,945	$ (501,330)	$ 206,677
Ending balance (in shares) at Jun. 30, 2018							67,753,667	55,404			67,753,667