Prepaid expenses and other current assets (Details) - USD ($)		Mar. 31, 2019	Dec. 31, 2018
Prepaid Expense and Other Assets, Current [Abstract]
Value added taxes receivables	[1]	$ 2,798,160	$ 4,700,702
Advances to suppliers	[2]	46,604,400	104,469,023
Interest receivable	[3]	840,767	826,729
Consideration for sales of Shanghai Sales	[4]	7,425,559	7,285,231
Receivables from Shanghai Sales for the prepayment to a supplier	[5]	16,081,972
Others	[6]	22,519,212	14,936,843
Total prepaid expenses and other current assets		$ 96,270,070	$ 132,218,528

[1] Value added taxes receivables mainly represent the input taxes on purchasing equipment by Heilongjiang Xinda Enterprise Group Company Limited ("HLJ Xinda Group") and Sichuan Xinda, which are to be net off with output taxes. Value added taxes receivables were recognized in operating activities in consolidated statements of cash flows.

[2] Advances to suppliers are the advances to purchase raw materials as of March 31, 2019.

[3] Interest receivable mainly represents interest income accrued from restricted cash.

[4] On December 18, 2018, HLJ Xinda Group entered into an agreement with Mr. Xiaohui Gao, General Manager of Heilongjiang Xinda Enterprise Group Shanghai New Materials Sales Company Limited ("Shanghai Sales"), to transfer the wholly owned equity from HLJ Xinda Group to Mr. Gao for a total consideration of RMB50.0 million (equivalent to US$7.4 million). Pursuant to the contract, the Company completed the legal transfer on December 19, 2018 and the full consideration of $7.4 million was received on April 11, 2019.

[5] In March 2019, HLJ Xinda Group entered into an agreement with Shanghai Sales, to transfer the proprietorship of the prepaid RMB108 million (equivalent to US$16.1 million) to Shanghai Caohejing Kangqiao Science & Green River Construction & Development Co., Ltd. ("Green River") to Shanghai Sales. Pursuant to the agreement, Shanghai Sales will pay the RMB108 million (equivalent to US$16.1 million) to HLJ Xinda Group by the end of June 2019. For details, please refer to Note 6.

[6] Others mainly include prepaid miscellaneous service fee and staff advance.