Other payables and accrued liabilities (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Other payables and accrued liabilities [Line Items]
Accrued expenses	$ 2,242,301	$ 1,140,443
Accrued payroll	10,506,404	7,442,056
Royalty payable	406,719	427,986
VAT payable	23,655	94,612
Sales deposits received	6,000,000	0
Contract liabilities	5,639,886	1,759,021
Other payables	1,041,738	1,379,227
Other payables and accrued liabilities	$ 25,860,703	$ 12,243,345