Warrants - Summary of outstanding warrants (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended			9 Months Ended		12 Months Ended	21 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Sep. 30, 2021	Jan. 19, 2021	May 29, 2020	Oct. 22, 2015
Class of Warrant or Right [Roll Forward]
Fair Value Adjustments	$ (812)		$ 3,354	$ (10,956)	$ 4,276
5-Year Private Warrants transferred to 5-Year Public Warrants		$ 284
Warrant liabilities
Class of Warrant or Right [Roll Forward]
Beginning balance (in shares)				22,610,316
Beginning balance				$ 15,389
Fair Value Adjustments				$ (10,955)
Transfers to an Unrelated Third Party (in shares)				(394,863)
Transfers to an Unrelated Third Party				$ (284)
Ending balance (in shares)	22,215,453			22,215,453		22,610,316	22,215,453
Ending balance	$ 4,150			$ 4,150		$ 15,389	$ 4,150
Outstanding warrants (in shares)	22,215,453			22,215,453		22,610,316	22,215,453
5-Year Private Warrants
Class of Warrant or Right [Roll Forward]
Beginning balance (in shares)				9,888,415
Beginning balance				$ 15,326
Fair Value Adjustments				$ (10,917)
Transfers to an Unrelated Third Party (in shares)				(394,863)		(351,585)	(746,448)
Transfers to an Unrelated Third Party				$ (284)
Ending balance (in shares)	9,493,552			9,493,552		9,888,415	9,493,552
Ending balance	$ 4,125			$ 4,125		$ 15,326	$ 4,125
Warrants, exercise price (in dollars per share)	$ 11.50			$ 11.50			$ 11.50
Warrant term	5 years			5 years			5 years
Outstanding warrants (in shares)	9,493,552			9,493,552		9,888,415	9,493,552
Seller Warrants
Class of Warrant or Right [Roll Forward]
Beginning balance (in shares)				12,721,901
Beginning balance				$ 63
Fair Value Adjustments				$ (38)
Transfers to an Unrelated Third Party (in shares)				0
Transfers to an Unrelated Third Party				$ 0
Ending balance (in shares)	12,721,901			12,721,901		12,721,901	12,721,901
Ending balance	$ 25			$ 25		$ 63	$ 25
Warrants, exercise price (in dollars per share)	$ 40.31			$ 40.31			$ 40.31	$ 40.31
Warrant term	7 years			7 years			7 years
Outstanding warrants (in shares)	12,721,901			12,721,901		12,721,901	12,721,901		12,700,000	12,721,901
Equity classified warrants
Class of Warrant or Right [Roll Forward]
Beginning balance (in shares)				33,984,817
Beginning balance				$ 41,557
Transfers to an Unrelated Third Party (in shares)				394,863
5-Year Private Warrants transferred to 5-Year Public Warrants				$ 284
Ending balance (in shares)	34,379,680			34,379,680		33,984,817	34,379,680
Ending balance	$ 41,841			$ 41,841		$ 41,557	$ 41,841
Outstanding warrants (in shares)	34,379,680			34,379,680		33,984,817	34,379,680
5-Year Public Warrants
Class of Warrant or Right [Roll Forward]
Beginning balance (in shares)				24,401,483
Beginning balance				$ 28,619
Transfers to an Unrelated Third Party (in shares)				394,863
5-Year Private Warrants transferred to 5-Year Public Warrants				$ 284
Ending balance (in shares)	24,796,346			24,796,346		24,401,483	24,796,346
Ending balance	$ 28,903			$ 28,903		$ 28,619	$ 28,903
Warrants, exercise price (in dollars per share)	$ 11.50			$ 11.50			$ 11.50
Warrant term	5 years			5 years			5 years
Outstanding warrants (in shares)	24,796,346			24,796,346		24,401,483	24,796,346
Public Offering Warrants
Class of Warrant or Right [Roll Forward]
Beginning balance (in shares)				9,583,334
Beginning balance				$ 12,938
Transfers to an Unrelated Third Party (in shares)				0
5-Year Private Warrants transferred to 5-Year Public Warrants				$ 0
Ending balance (in shares)	9,583,334			9,583,334		9,583,334	9,583,334
Ending balance	$ 12,938			$ 12,938		$ 12,938	$ 12,938
Warrants, exercise price (in dollars per share)	$ 10.50			$ 10.50			$ 10.50
Warrant term	5 years			5 years			5 years
Outstanding warrants (in shares)	9,583,334			9,583,334		9,583,334	9,583,334