Accounts Receivable - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Taxi commission revenue receivables	$ 1,200		$ 1,200
Changes in the allowance for doubtful accounts		$ 340	1,219
Accounts receivable	$ 1,559	1,559	1,219	$ 0
Guizhou Qianxi Green Environmentally Friendly Taxi Service Co
Accounts, Notes, Loans and Financing Receivable [Line Items]
Changes in the allowance for doubtful accounts		$ 300
Accounts receivable			$ 1,200