CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021
Current assets
Cash and cash equivalents	$ 39,462	$ 53,477	$ 70,578	$ 68,259	$ 77,563	$ 101,602	$ 115,005	$ 129,771
Marketable securities	0	0	0	8,462	13,371	0	0	0
Prepaid expenses and other current assets	3,509	3,081	2,874	7,680	7,558	5,895	7,564	8,256
Total current assets	42,971	56,558	73,452	84,401	98,492	107,497	122,569	138,027
Property and equipment, net	17,290	14,469	11,720	7,952	6,053	4,517	3,153	1,921
Other assets	4,286	3,660	3,804	3,946	4,087	4,225	4,366	1,628
Total assets	64,547	74,687	88,976	96,299	108,632	116,239	130,088	141,727
Current liabilities
Accounts payable	3,172	2,921	3,881	8,092	8,062	6,460	5,921	3,896
Accrued expenses and other current liabilities	13,343	14,993	18,826	16,722	19,971	17,620	11,728	9,151
Operating lease obligations	574	540	526	512	498	443	314	254
Total current liabilities	17,089	19,730	24,499	26,582	28,531	24,523	17,963	13,301
Non-current liabilities
Operating lease obligations, less current portion	3,567	3,164	3,308	3,449	3,587	3,764	3,892	1,180
Long term debt, net	2,800	1,495	1,472	1,058	2,289	2,265	1,750	1,731
Other non-current liabilities	527	497	455	309	244	0	0	0
Total non-current liabilities	6,894	5,156	5,235	4,816	6,120	6,029	5,642	2,911
Total liabilities	23,983	24,886	29,734	31,398	34,651	30,552	23,605	16,212
Commitments and contingencies (Note 15)
Stockholders' equity
Common stock; $0.01 par value; 295,000,000 shares authorized; 256,688,304 and 221,721,182 shares issued, and 256,566,804 and 221,599,682 shares outstanding at December 31, 2023 and 2022, respectively	2,567	2,566	2,566	2,265	2,217	2,168	2,163	2,158
Treasury stock, at cost, 121,500 shares at December 31, 2023 and 2022	(48)	(48)	(48)	(48)	(48)	(48)	(48)	(48)
Additional paid-in capital	324,191	322,452	320,181	303,073	294,874	284,231	281,139	278,704
Accumulated other comprehensive income	20	27	22	25	26	30	10	0
Accumulated deficit	(286,167)	(275,197)	(263,480)	(240,415)	(223,089)	(200,695)	(176,782)	(155,300)
Total stockholders' equity	40,564	49,801	59,242	64,901	73,981	85,687	106,483	125,515	$ 91,200
Total liabilities and stockholders' equity	64,547	74,687	88,976	96,299	108,632	116,239	130,088	141,727
Series A Convertible Preferred Stock
Stockholders' equity
Preferred stock issued	0	0	0	0	0	0	0	0
Series B Convertible Preferred Stock
Stockholders' equity
Preferred stock issued	$ 1	$ 1	$ 1	$ 1	$ 1	$ 1	$ 1	$ 1	$ 5,000