CONSOLIDATED STATEMENTS OF CHANGES IN REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Stockholders’ Notes Receivable	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Temporary equity, beginning balance (shares) at Dec. 31, 2016	11,330,704
Temporary equity, beginning balance at Dec. 31, 2016	$ 113,121
Increase (Decrease) in Temporary Equity
Issuance of redeemable convertible preferred stock, net of issuance costs (shares)	540,874
Issuance of redeemable convertible preferred stock, net of issuance costs	$ 5,427
Temporary equity, ending balance (shares) at Dec. 31, 2017	11,871,578
Temporary equity, ending balance at Dec. 31, 2017	$ 118,548
Stockholders' equity (deficit), beginning balance (shares) at Dec. 31, 2016		3,446,137
Stockholders' equity (deficit), beginning balance at Dec. 31, 2016	(108,733)	$ 1	$ 8,000	$ (521)	$ 472	$ (116,685)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of stock options (shares)		152,691
Issuance of common stock upon exercise of stock options	383		383
Issuance of common stock upon exercise of unvested stock options (shares)		4,312
Issuance of common stock upon exercise of unvested stock options	0
Stock-based compensation	1,438		1,438
Repayment of stockholders’ notes receivable	84			84
Forgiveness of stockholders’ note receivable	437			437
Vesting of early exercised stock options	122		122
Foreign currency translation	(70)				(70)
Unrealized gain of marketable securities	0
Net loss	(23,039)					(23,039)
Stockholders' equity (deficit), ending balance (shares) at Dec. 31, 2017		3,603,140
Stockholders' equity (deficit), ending balance at Dec. 31, 2017	$ (129,378)	$ 1	9,943	0	402	(139,724)
Increase (Decrease) in Temporary Equity
Conversion from preferred stock to common stock (shares)	(11,871,578)
Conversion from preferred stock to common stock	$ (118,548)
Temporary equity, ending balance (shares) at Dec. 31, 2018	0
Temporary equity, ending balance at Dec. 31, 2018	$ 0
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of stock options (shares)	395,117	289,077
Issuance of common stock upon exercise of stock options	$ 1,136		1,136
Issuance of common stock upon exercise of unvested stock options (shares)		106,028
Issuance of common stock upon exercise of unvested stock options	0
Conversion from preferred stock to common stock (shares)		12,066,654
Conversion from preferred stock to common stock	118,548	$ 1	118,547
Conversion from preferred stock warrants to common stock warrants	1,248		1,248
Issuance of common stock from warrants exercise (shares)		121,486
Issuance of common stock from warrants exercise	0
Issuance of common stock from IPO Proceeds, net (shares)		8,280,000
Issuance of common stock from IPO Proceeds, net	113,603	$ 1	113,602
Repurchase of unvested early exercised stock options (shares)		(15,628)
Repurchase of unvested early exercised stock options	0
Stock-based compensation	2,312		2,312
Vesting of early exercised stock options	139		139
Foreign currency translation	27				27
Unrealized gain of marketable securities	10				10
Net loss	(17,453)					(17,453)
Stockholders' equity (deficit), ending balance (shares) at Dec. 31, 2018		24,450,757
Stockholders' equity (deficit), ending balance at Dec. 31, 2018	$ 90,192	$ 3	$ 246,927	$ 0	$ 439	$ (157,177)