Consolidated Statements of Cash Flows - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Cash flows from operating activities:      
Net income (loss) $ (3,114,860) $ (6,177,438) $ 376,116
Share-based compensation expense 11,975,159 3,405,084 2,850,352
Depreciation of property and equipment 4,461,528 1,867,734 922,351
Changes in assets and liabilities, net of effects of businesses acquired:      
Accounts receivable (9,788,503) (4,807,207) (5,614,028)
Prepayments and other current assets (5,140,608) 206,559 47,809
Deferred tax assets 378,008 (336,463) (358,071)
Other non-current assets (691,093) (135,120) (338,478)
Accounts payable 1,753,706 1,121,563 806,508
Advances from customers 334,578 302,655 292,655
Taxes payable (450,594) 1,214,926 (1,134,236)
Accrued expenses and other liabilities 6,846,963 4,044,130 2,685,123
Net cash generated from operating activities 6,564,284 706,423 536,101
Cash flows from investing activities:      
Purchase of short-term investments (522,729,746) (97,558,282) (1,511,800)
Proceeds from sale and maturity of short-term investments 0 99,007,872 0
Purchase of property and equipment (12,879,553) (4,802,253) (2,260,791)
Cash received from an acquisition 556,361 0 0
Net cash and cash equivalents used in investing activities (535,052,938) (3,352,663) (3,772,591)
Cash flows from financing activities:      
Repurchase of ordinary shares 0 0 (784,799)
Proceeds from the initial public offering and concurrent private placement, net of underwriter discounts and commissions and other offering costs paid 483,628,037 0 0
Proceeds from exercise of stock options 10,000 0 0
Net cash and cash equivalents used in financing activities 533,638,039 0 65,771,809
Effect of foreign exchange rate changes on cash, cash equivalents and restricted cash 465,068 (268,646) (555,985)
Net increase (decrease) in cash, cash equivalents and restricted cash 5,614,453 (2,914,886) 61,979,334
Cash, cash equivalents and restricted cash at beginning of year 105,683,153 108,598,039 46,618,705
Cash, cash equivalents and restricted cash at end of year 111,297,606 105,683,153 108,598,039
Supplemental disclosure of cash flow information:      
Income taxes paid 742,049 411,068 421,560
Non-cash financing and investing activities:      
Accretion to redemption value of convertible redeemable preferred shares 193,465,743 50,714,953 33,234,811
Payables for property and equipment 2,292,922 613,463 366,503
Consideration payable for the acquisition 3,150,001 0 0
Proceeds receivable from exercise of employees’ share options 611,745 0 0
Deposits utilized for employees’ share option exercises (338,718) 0 0
Series C Preferred Stock      
Cash flows from financing activities:      
Proceeds from issuance of Series C and C+ convertible redeemable preferred shares, net of issuances costs 0 0 66,556,608
Series C+ Preferred Stock      
Cash flows from financing activities:      
Proceeds from issuance of Series C and C+ convertible redeemable preferred shares, net of issuances costs $ 50,000,002 $ 0 $ 0