CONDENSED CONSOLIDATED STATEMENT OF CHANGES IN STOCKHOLDERS' EQUITY (DEFICIT) (unaudited) - 9 months ended Sep. 30, 2017 - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Restricted Stock Units	Restricted Stock Units Common Stock
Balance, January 1, 2017 (in shares) at Dec. 31, 2016		34,274,718
Balance, January 1, 2017 at Dec. 31, 2016	$ (63,492)	$ 3		$ 1,330	$ (64,825)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(24,138)				(24,138)
Accretion of dividends on convertible preferred stock	(357)				(357)
Conversion of convertible preferred stock to common stock (in shares)		18,163,158
Conversion of convertible preferred stock to common stock	48,207	$ 2	$ 48,205
Conversion of convertible preferred stock warrant to common stock warrant	1,191		1,191
Issuance of common stock from initial public offering, net of issuance costs (in shares)		7,187,500
Issuance of common stock from initial public offering, net of issuance costs	$ 77,789	$ 1	77,788
Exercise of common stock warrant (in shares)		79,363
Issuance of common stock to directors (in shares)		10,841
Vesting of restricted stock units (in shares)						4,930	(4,930)
Exercise of stock options (in shares)	556,220	556,220
Exercise of stock options	$ 664		664
Stock-based compensation expense	10,919		10,919
Other comprehensive loss	(879)			(879)
Balance, September 30, 2017 (in shares) at Sep. 30, 2017		60,276,730
Balance, September 30, 2017 at Sep. 30, 2017	$ 49,904	$ 6	$ 138,767	$ 451	$ (89,320)