Organization and Nature of Operations - Financial Information of VIEs (Details) - USD ($)
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Current assets:      
Cash and cash equivalents $ 111,217,606 $ 105,603,153  
Short-term investments 524,220,154 0  
Accounts receivable, net 27,840,149 16,247,565  
Prepayments and other current assets 7,458,832 1,381,037  
Total current assets 670,736,741 123,231,755  
Non-current assets:      
Property and equipment, net 16,753,850 6,281,990  
Deferred tax assets 510,500 836,514  
Other non-current assets 1,603,937 808,862  
Total non-current assets 22,166,996 7,927,366  
Total assets 692,903,737 131,159,121  
Current liabilities:      
Accounts payable 7,721,368 4,088,283  
Amounts due to related parties 1,150,000 0  
Advances from customers 1,338,516 920,925  
Taxes payable 2,171,280 2,493,137  
Total current liabilities 36,306,687 18,481,277  
Total liabilities 36,440,575 18,481,277  
Income Statement [Abstract]      
Total revenues 133,563,921 64,428,690 $ 43,656,954
Net income (loss) (3,114,860) (6,177,438) 376,116
Statement of Cash Flows [Abstract]      
Net cash and cash equivalents generated from operating activities 6,564,284 706,423 536,101
Net cash and cash equivalents used in investing activities (535,052,938) (3,352,663) (3,772,591)
Net cash and cash equivalents used in financing activities 533,638,039 0 65,771,809
VIE      
Current assets:      
Cash and cash equivalents 2,362,068 17,308,887  
Short-term investments 12,413,983 0  
Accounts receivable, net 23,557,994 14,827,841  
Amounts due from related parties 2,090,321 2,445,447  
Prepayments and other current assets 2,704,275 886,022  
Total current assets 43,128,641 35,468,197  
Non-current assets:      
Property and equipment, net 8,951,306 3,292,978  
Deferred tax assets 510,500 387,950  
Other non-current assets 205,147 69,968  
Total non-current assets 9,666,953 3,750,896  
Total assets 52,795,594 39,219,093  
Current liabilities:      
Accounts payable 5,336,880 2,992,628  
Amounts due to related parties 34,198,167 27,780,440  
Advances from customers 1,112,800 733,518  
Taxes payable 253,617 756,020  
Accrued expenses and other current liabilities 5,035,100 3,440,748  
Total current liabilities 45,936,564 35,703,354  
Total liabilities 45,936,564 35,703,354  
Income Statement [Abstract]      
Total revenues 115,831,093 57,444,924 37,172,123
Net income (loss) 1,247,450 224,905 (146,806)
Statement of Cash Flows [Abstract]      
Net cash and cash equivalents generated from operating activities 3,918,250 9,389,954 2,774,063
Net cash and cash equivalents used in investing activities (18,865,069) (998,141) (2,251,153)
Net cash and cash equivalents used in financing activities $ 0 $ 0 $ 0