Accrued expenses and other current liabilities (Schedule of Accrued expenses and other current liabilities) (Details) - USD ($)		Mar. 31, 2019	Dec. 31, 2018
Accrued Liabilities, Current [Abstract]
Payables for purchase of property, plant and equipment		$ 12,922,814	$ 53,059,897
Accrued freight expenses		31,252,409	25,908,990
Accrued interest expenses		12,628,239	8,873,532
Contract liabilities	[1]	1,775,010	16,105,245
Non income tax payables		4,049,713	6,425,236
Others	[2]	19,795,699	16,553,998
Total accrued expenses and other current liabilities		$ 82,423,884	$ 126,926,898

[1] Contract liabilities mainly represent the advance received from customers in the PRC for the finished goods and raw materials purchases as of March 31, 2019. The change in contract liabilities primarily represents the cash received, less amounts recognized as revenues during the period.

[2] Others mainly represent accrued payroll and employee benefits, accrued audit and consulting fees, electricity fee and other accrued miscellaneous operating expenses.