Cash, cash equivalents, and Restricted cash (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 83,408,816	$ 53,583,898	$ 71,537,108	$ 67,209,753
Restricted cash - current	1,872,244	5,471,470	0	0
Restricted cash - noncurrent	0	74,917	29,586,342	10,953,885
Total cash, cash equivalents and restricted cash shown in the condensed consolidated statements of cash flows	$ 85,281,060	$ 59,130,285	$ 101,123,450	$ 78,163,638