Note 3 - Accounts Receivable, Net - Accounts Receivable (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts receivable	$ 50,651,104	$ 15,064,580
Less: allowance for doubtful accounts	(623,970)	(658,104)	$ (567,108)
Accounts receivable, net	$ 50,027,134	$ 14,406,476

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.

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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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