Accounts receivable, net - Schedule of Accounts Receivable (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts receivable, net
Accounts receivable	$ 32,312,000	$ 35,137,000
Less: Allowance for credit losses	(9,329,000)	(7,604,000)	$ (7,709,000)	$ (31,000)
Accounts receivable, net	$ 22,983,000	$ 27,533,000

Amount, after allowance for credit loss, of right to consideration from customer for product sold and service rendered in normal course of business, classified as current.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-Publisher FASB
-Name Accounting Standards Codification
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