Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash Flows from Operating Activities
Net loss	$ (125,551)	$ (66,150)	$ (77,187)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	16,395	7,899	8,353
Operating lease right-of-use asset amortization	1,962	1,775	1,792
Net amortization of premium (accretion of discount) on marketable securities	1,830	37	(594)
Depreciation and amortization	813	948	732
Change in deferred tax asset		1,438	(775)
Loss on early repayment of debt		585
Gain on disposal of property and equipment			8
Changes in operating assets and liabilities:
Research and development tax incentive receivable	(1,775)	(990)	1,411
Receivable from collaboration partner - related party	860	4,329	(2,168)
Prepaid expenses and other assets	(3,227)	(1,102)	(2,820)
Accounts payable	(1,390)	309	(3,000)
Payable to collaboration partner - related party	(1,833)	1,471	201
Accrued expenses and other payables	19,097	5,840	1,098
Deferred revenue - related party	(12,876)	(27,053)	33,307
Operating lease liability	(2,049)	(1,941)	(1,885)
Other liabilities	(121)	121
Net cash used in operating activities	(107,865)	(72,484)	(41,527)
Cash Flows from Investing Activities
Purchase of marketable securities	(286,589)	(280,027)	(166,936)
Proceeds from maturities of marketable securities	271,830	189,533	114,193
Purchases of property and equipment	(1,101)	(471)	(967)
Net cash used in investing activities	(15,860)	(90,965)	(53,710)
Cash Flows from Financing Activities
Proceeds from public offering of common stock, net of issuance costs	123,829	213,303
Proceeds from issuance of common stock upon exercise of stock options and purchases under employee stock purchase plan	6,283	2,799	1,779
Tax withholding payments related to net settlement of restricted stock units	(189)
Proceeds from at-the-market offering, net of issuance costs		42,062	34,492
Early repayment of long-term debt		(10,524)
Issuance costs related to long-term debt		(14)
Proceeds from issuance of long-term debt, net of issuance costs			9,765
Net cash provided by financing activities	129,923	247,626	46,036
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(126)	175	(26)
Net increase (decrease) in cash, cash equivalents and restricted cash	6,072	84,352	(49,227)
Cash, cash equivalents and restricted cash, beginning of period	117,818	33,466	82,693
Cash, cash equivalents and restricted cash, end of period	123,890	117,818	33,466
Supplemental Disclosure of Non-Cash Financing and Investing Information:
Cash paid for interest		438	70
Purchases of property and equipment in accounts payable and accrued liabilities	143	85	100
Public Offering | Accrued liabilities and other payables
Supplemental Disclosure of Non-Cash Financing and Investing Information:
Issuance costs related to common stock offering	$ 25	205	$ 80
Public Offering | Prepaid expenses and other assets
Supplemental Disclosure of Non-Cash Financing and Investing Information:
Issuance costs related to common stock offering		124
At-the-market offering | Prepaid expenses and other assets
Supplemental Disclosure of Non-Cash Financing and Investing Information:
Issuance costs related to common stock offering		$ 191