Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	At The Market Equity Offering Program	Equity Purchase Agreement Lincoln Park Capital Fund LLC	Loan Agreement Hercules Capital	Common Stock	Common Stock At The Market Equity Offering Program	Common Stock Equity Purchase Agreement Lincoln Park Capital Fund LLC	Common Stock Loan Agreement Hercules Capital	Additional Paid-In Capital	Additional Paid-In Capital At The Market Equity Offering Program	Additional Paid-In Capital Equity Purchase Agreement Lincoln Park Capital Fund LLC	Additional Paid-In Capital Loan Agreement Hercules Capital	Related Party Promissory Notes for Purchase of Common Stock	Employee Promissory Notes for Purchase of Common Stock	Accumulated Other Comprehensive Gain (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2018	$ 160,693				$ 4				$ 324,663				$ (201)	$ (400)	$ (95)	$ (163,278)
Beginning balance, (in shares) at Dec. 31, 2018					42,414,294
Issuance of common stock, net of issuance costs		$ 26,086				$ 1				$ 26,085
Issuance of common stock (in shares)						3,974,908
Issuance of common stock upon exercise of stock options	840								840
Issuance of common stock upon exercise of stock options (in shares)					505,226
Vesting of early exercised stock options	647								647
Stock-based compensation	10,852								10,852
Common stock issued to third parties	2,995								3,022				(9)	(18)
Common stock issued to third parties, (in shares)					253,334
Repurchased shares (in shares)					(4,281)
Issuance of common stock under employee stock purchase plan (“2018 ESPP”)	586								586
Issuance of common stock under employee stock purchase plan ("2018 ESPP") (in Shares)					83,584
Unrealized gain (loss) on available-for-sale marketable securities	185														185
Net loss	(82,177)															(82,177)
Ending balance at Dec. 31, 2019	120,707				$ 5				366,695				(210)	(418)	90	(245,455)
Ending balance, (in shares) at Dec. 31, 2019					47,227,065
Issuance of common stock, net of issuance costs		37,270								37,270
Issuance of common stock (in shares)						5,002,257
Issuance of common stock upon exercise of stock options	1,510								1,510
Issuance of common stock upon exercise of stock options (in shares)					410,484
Issuance of common stock upon vesting of restricted stock units (in shares)					103,020
Vesting of early exercised stock options	216								216
Stock-based compensation	13,746								13,746
Common stock issued for services	100								100
Common stock issued for services (in shares)					43,550
Common stock issued to third parties for milestone payments	2,310								2,310
Common stock issued to third parties for milestone payments, (in shares)					361,644
Repayment of promissory note from employee from purchase of common stock	374													374
Repayment of promissory note from employee through repurchase of early exercise shares									(44)					$ 44
Repayment of promissory note from employee through repurchase of early exercise shares (in shares)					(12,909)
Issuance of common stock under employee stock purchase plan (“2018 ESPP”)	576								576
Issuance of common stock under employee stock purchase plan ("2018 ESPP") (in Shares)					118,102
Unrealized gain (loss) on available-for-sale marketable securities	(85)														(85)
Net loss	(93,844)															(93,844)
Ending balance at Dec. 31, 2020	$ 82,880				$ 5				422,379				(210)		5	(339,299)
Ending balance, (in shares) at Dec. 31, 2020	53,253,213				53,253,213
Issuance of common stock, net of issuance costs		$ 10,357	$ 9,040	$ 2,704			$ 1			$ 10,357	$ 9,039	$ 2,704
Issuance of common stock (in shares)			2,900,000			1,894,527	4,172,855	1,727,361
Issuance of common stock upon exercise of stock options	$ 1,795								1,795
Issuance of common stock upon exercise of stock options (in shares)	430,047				497,538
Repurchase of early exercised shares, (in shares)					(33,370)
Vesting of restricted stock units, (in shares)					962,693
Stock-based compensation	$ 11,553								11,553
Common stock issued to third parties	1,457								1,457
Common stock issued to third parties, (in shares)					400,052
Repayment of promissory note from employee from purchase of common stock	210												$ 210
Issuance of common stock under employee stock purchase plan (“2018 ESPP”)	347								347
Issuance of common stock under employee stock purchase plan ("2018 ESPP") (in Shares)					117,037
Unrealized gain (loss) on available-for-sale marketable securities	(49)														(49)
Net loss	(60,725)															(60,725)
Ending balance at Dec. 31, 2021	$ 59,569				$ 6				$ 459,631						$ (44)	$ (400,024)
Ending balance, (in shares) at Dec. 31, 2021	62,991,906				62,991,906