Lease - Balances reported in the consolidated balance sheets related to the Group's leases (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Lease
Operating lease right-of-use assets	$ 7,280,763	$ 5,732,559
Operating lease liabilities	$ 7,207,293	$ 5,841,658

Present value of lessee's discounted obligation for lease payments from operating lease.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121603541&loc=SL77918627-209977

Name:	us-gaap_OperatingLeaseLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant