Consolidated 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	$ (54,630)	$ (41,742)	$ (35,087)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,510	1,544	1,301
Stock-based compensation	7,596	4,943	4,007
Amortization of premiums and discounts on marketable securities	1,770	317	(979)
Amortization of debt discount and issuance costs and other non-cash interest	91
Changes in operating assets and liabilities
Prepaid expenses and other current assets	1,051	(1,424)	(553)
Accounts payable and accrued liabilities	1,217	313	2,208
Operating lease liabilities and other liabilities	(1,042)	(900)	(774)
Net cash used in operating activities	(42,437)	(36,949)	(29,877)
Cash flows from investing activities:
Purchases of property and equipment	(316)	(194)	(607)
Purchases of marketable securities	(156,378)	(225,728)	(102,255)
Maturities of marketable securities	128,250	169,424	123,281
Net cash (used in) provided by investing activities	(28,444)	(56,498)	20,419
Cash flows from financing activities:
Proceeds from long-term debt, net of debt discount and issuance costs of $469	9,531
Proceeds from issuance of common stock under at-the-market offerings, net of issuance costs	100,970
Proceeds from sale of common stock and pre-funded warrants in public offerings, net of offering costs		99,186
Proceeds from issuance of common stock under employee stock incentive plans	2,084	456	272
Net cash provided by financing activities	112,585	99,642	272
Effect of exchange rate changes on cash and cash equivalents	(50)	82	(45)
Net increase (decrease) in cash and cash equivalents	41,654	6,277	(9,231)
Cash and cash equivalents at the beginning of period	21,228	14,951	24,182
Cash and cash equivalents at the end of period	62,882	21,228	14,951
Supplemental disclosures of noncash investing and financing information:
Reclassification of employee stock liability to equity upon vesting	21	41	$ 50
Purchase of property and equipment in accounts payable	442
Unpaid offering costs in accrued liabilities		$ 25
Supplemental disclosures
Cash paid for interest	$ 69