Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders Equity (Deficit) - USD ($) $ in Thousands	Total	Series A and A-1 Redeemable Convertible Preferred Stock	Initial Public Offering	Private Placement Novartis Institutes for Biomedical Research, Inc.	Common Stock	Common Stock Initial Public Offering	Common Stock Private Placement Novartis Institutes for Biomedical Research, Inc.	Additional Paid-in Capital	Additional Paid-in Capital Initial Public Offering	Additional Paid-in Capital Private Placement Novartis Institutes for Biomedical Research, Inc.	Note Receivable From Officer	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance at Dec. 31, 2016	$ (26,912)							$ 2,040			$ (31)	$ (353)	$ (28,568)
Temporary equity beginning balance, share at Dec. 31, 2016		37,100,000
Temporary equity beginning balance at Dec. 31, 2016		$ 48,477
Beginning balance, share at Dec. 31, 2016					2,399,265
Issuance of common stock upon exercise of stock options	102							102
Issuance of common stock upon exercise of stock options, share					287,085
Vesting of restricted common stock	35							35
Stock-based compensation expense	4,709							4,709
Collection of note receivable from officer	62							31			$ 31
Accretion of redeemable convertible preferred stock to redemption value		40
Accretion of redeemable convertible preferred stock to redemption value	(40)							(40)
Unrealized gain on marketable securities	107											107
Net income (loss)	(45,377)												(45,377)
Ending balance at Dec. 31, 2017	$ (67,314)							6,877				(246)	(73,945)
Temporary equity ending balance, share at Dec. 31, 2017	37,100,000
Temporary equity ending balance at Dec. 31, 2017	$ 48,517
Ending balance, share at Dec. 31, 2017					2,686,350
Issuance of common stock upon exercise of stock options	467							467
Issuance of common stock upon exercise of stock options, share					272,895
Repurchases of unvested restricted stock, shares					(16,935)
Stock-based compensation expense	5,217							5,217
Accretion of redeemable convertible preferred stock to redemption value		$ 11
Accretion of redeemable convertible preferred stock to redemption value	(11)							(11)
Conversion of redeemable convertible preferred stock to common stock	48,528				$ 2			48,526
Temporary equity conversion of convertible preferred stock, shares		(37,100,000)
Temporary equity conversion of convertible preferred stock		$ (48,528)
Conversion of convertible preferred stock, shares					16,863,624
Issuance of common stock			$ 97,209	$ 11,500		$ 1			$ 97,208	$ 11,500
Issuance of common stock, shares						7,200,000	766,666
Adjustment due to the adoption of ASC 606	13,736												13,736
Unrealized gain on marketable securities	127											127
Net income (loss)	(6,597)												(6,597)
Ending balance at Dec. 31, 2018	$ 102,862				$ 3			169,784				(119)	(66,806)
Ending balance, share at Dec. 31, 2018	27,772,600				27,772,600
Issuance of common stock upon exercise of stock options	$ 255							255
Issuance of common stock upon exercise of stock options, share					110,156
Stock-based compensation expense	5,991							5,991
Issuance of common stock	24							24
Issuance of common stock, shares					10,581
Portion of convertible note payable proceeds allocated to beneficial conversion feature	2,101							2,101
Unrealized gain on marketable securities	222											222
Net income (loss)	(54,789)												(54,789)
Ending balance at Dec. 31, 2019	$ 56,666				$ 3			$ 178,155				$ 103	$ (121,595)
Ending balance, share at Dec. 31, 2019	27,893,337				27,893,337