Summary of Significant Accounting Policies - Cash, Cash Equivalents and Restricted Cash (Details) - USD ($)	6 Months Ended
Jun. 30, 2021	Dec. 31, 2020
Cash, Cash Equivalents and Restricted Cash
Restricted cash - current portion	$ 3,293,189	$ 3,264,145
Guarantee deposit for loan facility provided by the bank	3,100,000
Long-term restricted cash	$ 21,700,000	$ 21,689,436

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