Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating activities
Net loss	$ (60,725)	$ (93,844)	$ (82,177)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,880	3,449	2,663
Amortization of debt issuance costs	813	318	0
Debt extinguishment gain upon conversion to equity	(123)	0	0
Net accretion and amortization of premium and discounts on marketable securities	1,043	256	(1,151)
Other expense related to the commitment shares issued to Lincoln Park Capital Fund	825	0	0
Stock-based compensation	11,553	13,813	10,852
Common stock issued to third parties	1,457	1,211	965
Non-cash rent expense	(2,152)	(1,076)	0
Impairment of long-lived assets	0	2,629	0
Change in fair value of strategic investment	0	(502)	(4,507)
Accretion of tenant improvement allowance	0	0	(1,275)
Change in fair value of contingent consideration	0	(33)	(1,352)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	1,288	(1,168)	(169)
Other long-term assets	(91)	628	(31)
Accounts payable	(573)	(2,640)	(227)
Accrued compensation	(1,327)	(517)	2,114
Accrued liabilities and other current liabilities	(1,131)	(857)	(587)
Other long-term liabilities	24	0	0
Derivative liability related to debt	963	0	0
Deferred revenue	216	0	0
Deferred rent, net of current portion	0	0	2,461
Net cash used in operating activities	(45,060)	(78,333)	(72,421)
Investing activities
Purchase of marketable securities	(81,492)	(138,486)	(119,270)
Maturities of marketable securities	121,000	127,915	188,809
Sale of strategic investments	0	6,009	0
Purchase of property and equipment	(195)	(646)	(1,586)
Net cash provided by (used in) investing activities	39,313	(5,208)	67,953
Financing activities
Proceeds from repayment of employee promissory notes	210	374	0
Proceeds from long-term debt, net of issuance costs to lender	0	24,550	0
Payment of long-term debt non-lender issuance costs	0	(360)	0
Proceeds from issuance of common stock upon exercise of stock options, net of repurchases	1,784	1,510	840
Proceeds from issuance of common stock under the 2018 ESPP	347	576	586
Current portion of long-term debt arrangement	(68)	0	0
Payments made on capital lease obligations	0	(45)	(73)
Net cash provided by financing activities	20,845	63,875	27,438
Net increase (decrease) in cash, cash equivalents and restricted cash	15,098	(19,666)	22,970
Cash, cash equivalents and restricted cash at beginning of year	19,253	38,919	15,949
Cash, cash equivalents and restricted cash at end of year	34,351	19,253	38,919
Supplemental Disclosures of Cash Flow Information:
Cash paid for interest	2,370	773	0
Supplemental Disclosures of Non-Cash Investing and Financing Activities
Issuance of common shares in payment of debt	2,704	0	0
Property and equipment included in accounts payable	0	13	565
Issuance of common stock in settlement of contingent consideration milestone	0	1,098	0
Issuance of shares in settlement of share-based liability	0	100	0
Right-of-use assets obtained in exchange for new operating lease liabilities	0	27,714	0
Lessor funded lease incentives included in property and equipment	0	0	10,651
Receipt of promissory note from related party for purchase of common stock	0	0	27
ATM Offering Program
Financing activities
Proceeds from issuance of common stock, net of issuance costs	10,357	37,270	26,085
Lincoln Park Capital Fund
Financing activities
Proceeds from issuance of common stock, net of issuance costs	$ 8,215	$ 0	$ 0