Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders’ Deficit - USD ($) | Common Stock | Additional Paid-in capital | Accumulated other comprehensive loss | Accumulated deficit | Series A convertible preferred stock | Series B convertible preferred stock | Series C convertible preferred stock | Total |
Temporary equity, beginning balance at Dec. 31, 2018 | | | | | $ 6,483,044 | $ 49,742,942 | $ 56,364,645 | |
Temporary Equity, Beginning Balance (in shares) at Dec. 31, 2018 | | | | | 612,446 | 7,235,969 | 4,712,698 | |
Increase (Decrease) in Temporary Equity | | | | | | | | |
Issuance of convertible preferred stock, net of issuance costs | | | | | | | $ 5,598,362 | |
Issuance of convertible preferred stock (in shares) | | | | | | | 467,179 | |
Temporary equity, ending balance at Jun. 30, 2019 | | | | | $ 6,483,044 | $ 49,742,942 | $ 61,963,007 | |
Temporary Equity, Ending Balance (in shares) at Jun. 30, 2019 | | | | | 612,446 | 7,235,969 | 5,179,877 | |
Equity, beginning balance at Dec. 31, 2018 | $ 127,091 | $ 19,666,588 | $ (8,761,325) | $ (62,468,456) | | | | $ (51,436,102) |
Equity, beginning balance (in shares) at Dec. 31, 2018 | 1,155,366 | | | | | | | |
Increase (Decrease) in Stockholders' Equity | | | | | | | | |
Exercise of stock options | $ 2,883 | 20,235 | | | | | | 23,118 |
Exercise of stock options (in shares) | 26,207 | | | | | | | |
Stock‑based compensation | | 284,909 | | | | | | 284,909 |
Foreign currency translation | | | (1,986,667) | | | | | (1,986,667) |
Net loss | | | | (8,737,650) | | | | (8,737,650) |
Equity, ending balance at Jun. 30, 2019 | $ 129,974 | 19,971,732 | (10,747,992) | (71,206,106) | | | | (61,852,392) |
Equity, ending balance (in shares) at Jun. 30, 2019 | 1,181,573 | | | | | | | |
Temporary equity, beginning balance at Dec. 31, 2018 | | | | | $ 6,483,044 | $ 49,742,942 | $ 56,364,645 | |
Temporary Equity, Beginning Balance (in shares) at Dec. 31, 2018 | | | | | 612,446 | 7,235,969 | 4,712,698 | |
Equity, beginning balance at Dec. 31, 2018 | $ 127,091 | 19,666,588 | (8,761,325) | (62,468,456) | | | | (51,436,102) |
Equity, beginning balance (in shares) at Dec. 31, 2018 | 1,155,366 | | | | | | | |
Increase (Decrease) in Stockholders' Equity | | | | | | | | |
Foreign currency translation | | | | | | | | (4,926,841) |
Net loss | | | | | | | | (14,987,069) |
Equity, ending balance at Sep. 30, 2019 | $ 1,182 | 20,346,849 | (13,688,166) | (77,455,525) | $ 6,483,044 | $ 49,742,942 | $ 61,963,007 | (70,795,660) |
Equity, ending balance (in shares) at Sep. 30, 2019 | 1,181,733 | | | | 612,446 | 7,235,969 | 5,179,877 | |
Temporary equity, beginning balance at Jun. 30, 2019 | | | | | $ 6,483,044 | $ 49,742,942 | $ 61,963,007 | |
Temporary Equity, Beginning Balance (in shares) at Jun. 30, 2019 | | | | | 612,446 | 7,235,969 | 5,179,877 | |
Equity, beginning balance at Jun. 30, 2019 | $ 129,974 | 19,971,732 | (10,747,992) | (71,206,106) | | | | (61,852,392) |
Equity, beginning balance (in shares) at Jun. 30, 2019 | 1,181,573 | | | | | | | |
Increase (Decrease) in Stockholders' Equity | | | | | | | | |
Issuance of common stock | $ 100 | | | | | | | 100 |
Issuance of common stock (in shares) | 160 | | | | | | | |
Stock‑based compensation | | 246,225 | | | | | | 246,225 |
Foreign currency translation | | | (2,940,174) | | | | | (2,940,174) |
Exchange of preferred and common stock of Aprea Therapeutics AB into stock of Aprea Therapeutics, Inc. | $ (128,892) | 128,892 | | | | | | |
Net loss | | | | (6,249,419) | | | | (6,249,419) |
Equity, ending balance at Sep. 30, 2019 | $ 1,182 | 20,346,849 | (13,688,166) | (77,455,525) | $ 6,483,044 | $ 49,742,942 | $ 61,963,007 | (70,795,660) |
Equity, ending balance (in shares) at Sep. 30, 2019 | 1,181,733 | | | | 612,446 | 7,235,969 | 5,179,877 | |
Equity, beginning balance at Dec. 31, 2019 | $ 21,023 | 226,284,548 | (11,533,778) | (90,528,263) | | | | 124,243,530 |
Equity, beginning balance (in shares) at Dec. 31, 2019 | 21,022,752 | | | | | | | |
Increase (Decrease) in Stockholders' Equity | | | | | | | | |
Exercise of stock options | $ 164 | 150,785 | | | | | | 150,949 |
Exercise of stock options (in shares) | 164,075 | | | | | | | |
Stock‑based compensation | | 2,161,931 | | | | | | 2,161,931 |
Foreign currency translation | | | (667,870) | | | | | (667,870) |
Net loss | | | | (25,768,184) | | | | (25,768,184) |
Equity, ending balance at Jun. 30, 2020 | $ 21,187 | 228,597,264 | (12,201,648) | (116,296,447) | | | | 100,120,356 |
Equity, ending balance (in shares) at Jun. 30, 2020 | 21,186,827 | | | | | | | |
Equity, beginning balance at Dec. 31, 2019 | $ 21,023 | 226,284,548 | (11,533,778) | (90,528,263) | | | | 124,243,530 |
Equity, beginning balance (in shares) at Dec. 31, 2019 | 21,022,752 | | | | | | | |
Increase (Decrease) in Stockholders' Equity | | | | | | | | |
Foreign currency translation | | | | | | | | (836,852) |
Net loss | | | | | | | | (38,086,266) |
Equity, ending balance at Sep. 30, 2020 | $ 21,187 | 229,986,911 | (12,370,630) | (128,614,529) | | | | 89,022,939 |
Equity, ending balance (in shares) at Sep. 30, 2020 | 21,186,827 | | | | | | | |
Equity, beginning balance at Jun. 30, 2020 | $ 21,187 | 228,597,264 | (12,201,648) | (116,296,447) | | | | 100,120,356 |
Equity, beginning balance (in shares) at Jun. 30, 2020 | 21,186,827 | | | | | | | |
Increase (Decrease) in Stockholders' Equity | | | | | | | | |
Stock‑based compensation | | 1,389,647 | | | | | | 1,389,647 |
Foreign currency translation | | | (168,982) | | | | | (168,982) |
Net loss | | | | (12,318,082) | | | | (12,318,082) |
Equity, ending balance at Sep. 30, 2020 | $ 21,187 | $ 229,986,911 | $ (12,370,630) | $ (128,614,529) | | | | $ 89,022,939 |
Equity, ending balance (in shares) at Sep. 30, 2020 | 21,186,827 | | | | | | | |