Cash, cash equivalents, and Restricted cash (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 100,011,694	$ 69,927,594	$ 83,408,816	$ 53,583,898
Restricted cash - current	25,557,674	18,846,177	1,872,244	5,471,470
Restricted cash - noncurrent	75,000	75,000	0	74,917
Total cash, cash equivalents and restricted cash shown in the condensed consolidated statements of cash flows	$ 125,644,368	$ 88,848,771	$ 85,281,060	$ 59,130,285

Amount of cash and cash equivalents restricted as to withdrawal or usage, classified as noncurrent. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Name:	us-gaap_RestrictedCashAndCashEquivalentsNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant