Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Loss [Member]
Beginning balance at Dec. 31, 2019	$ (694)	$ 6	$ 22,432	$ (23,132)
Beginning balance, shares at Dec. 31, 2019		6,091,250
Capital contributions from related party	9,595		9,595
Stock-based compensation expense	29		29
Net loss	(6,674)			(6,674)
Ending balance at Mar. 31, 2020	2,256	$ 6	32,056	(29,806)
Ending balance, shares at Mar. 31, 2020		6,091,250
Beginning balance at Dec. 31, 2019	(694)	$ 6	22,432	(23,132)
Beginning balance, shares at Dec. 31, 2019		6,091,250
Capital contributions from related party	17,995
Unrealized gain (loss) on marketable debt securities	(2)
Net loss	(28,278)
Ending balance at Sep. 30, 2020	102,641	$ 15	154,038	(51,410)	$ (2)
Ending balance, shares at Sep. 30, 2020		15,356,206
Beginning balance at Mar. 31, 2020	2,256	$ 6	32,056	(29,806)
Beginning balance, shares at Mar. 31, 2020		6,091,250
Capital contributions from related party	8,400		8,400
Merger with Zafgen Inc.	37,119	$ 3	37,116
Merger with Zafgen Inc., Shares		3,124,337
Private Placement of common shares and pre-funded warrants, net of transaction costs	75,350	$ 6	75,344
Shares issued to private placement, Shares		6,140,619
Stock-based compensation expense	752		752
Unrealized gain (loss) on marketable debt securities	(3)				(3)
Net loss	(11,330)			(11,330)
Ending balance at Jun. 30, 2020	112,544	$ 15	153,668	(41,136)	(3)
Ending balance, shares at Jun. 30, 2020		15,356,206
Stock-based compensation expense	370		370
Unrealized gain (loss) on marketable debt securities	1				1
Net loss	(10,274)			(10,274)
Ending balance at Sep. 30, 2020	102,641	$ 15	154,038	(51,410)	(2)
Ending balance, shares at Sep. 30, 2020		15,356,206
Beginning balance at Dec. 31, 2020	89,692	$ 15	155,290	(65,614)	1
Beginning balance, shares at Dec. 31, 2020		15,367,730
Stock-based compensation expense	1,180		1,180
Net loss	(12,088)			(12,088)
Ending balance at Mar. 31, 2021	78,784	$ 15	156,470	(77,702)	1
Ending balance, shares at Mar. 31, 2021		15,367,730
Beginning balance at Dec. 31, 2020	89,692	$ 15	155,290	(65,614)	1
Beginning balance, shares at Dec. 31, 2020		15,367,730
Unrealized gain (loss) on marketable debt securities	(1)
Net loss	(41,502)
Ending balance at Sep. 30, 2021	72,067	$ 18	179,165	(107,116)
Ending balance, shares at Sep. 30, 2021		17,710,450
Beginning balance at Mar. 31, 2021	78,784	$ 15	156,470	(77,702)	1
Beginning balance, shares at Mar. 31, 2021		15,367,730
Stock-based compensation expense	1,350		1,350
Net loss	(12,609)			(12,609)
Ending balance at Jun. 30, 2021	67,525	$ 15	157,820	(90,311)	1
Ending balance, shares at Jun. 30, 2021		15,367,730
Stock-based compensation expense	1,463		1,463
Issuance of Common Stock, net	19,885	$ 3	19,882
Issuance of Common Stock, net, Shares		2,342,720
Unrealized gain (loss) on marketable debt securities	(1)				$ (1)
Net loss	(16,805)			(16,805)
Ending balance at Sep. 30, 2021	$ 72,067	$ 18	$ 179,165	$ (107,116)
Ending balance, shares at Sep. 30, 2021		17,710,450