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, 2017					$ 6,483,044	$ 49,742,942
Temporary Equity, Beginning Balance (in shares) at Dec. 31, 2017					612,446	7,235,969
Temporary Equity, Ending Balance at Jun. 30, 2018					$ 6,483,044	$ 49,742,942
Temporary Equity, Ending Balance (in shares) at Jun. 30, 2018					612,446	7,235,969
Equity, Beginning Balance at Dec. 31, 2017	$ 126,838	$ 19,335,560	$ (8,287,406)	$ (46,940,187)				$ (35,765,195)
Equity, Beginning Balance (in shares) at Dec. 31, 2017	1,153,061
Increase (Decrease) in Stockholders' Equity
Exercise of stock options	$ 165	1,250						1,415
Exercise of stock options (in shares)	1,503
Stock based compensation		169,854						169,854
Foreign currency translation			(1,176,208)					(1,176,208)
Net loss				(7,710,338)				(7,710,338)
Equity, Ending Balance at Jun. 30, 2018	$ 127,003	19,506,664	(9,463,614)	(54,650,525)				(44,480,472)
Equity, Ending Balance (in shares) at Jun. 30, 2018	1,154,564
Temporary Equity, Beginning Balance at Dec. 31, 2017					$ 6,483,044	$ 49,742,942
Temporary Equity, Beginning Balance (in shares) at Dec. 31, 2017					612,446	7,235,969
Temporary Equity, Ending Balance at Sep. 30, 2018					$ 6,483,044	$ 49,742,942
Temporary Equity, Ending Balance (in shares) at Sep. 30, 2018					612,446	7,235,969
Equity, Beginning Balance at Dec. 31, 2017	$ 126,838	19,335,560	(8,287,406)	(46,940,187)				(35,765,195)
Equity, Beginning Balance (in shares) at Dec. 31, 2017	1,153,061
Increase (Decrease) in Stockholders' Equity
Foreign currency translation								(1,110,408)
Net loss								(10,848,601)
Equity, Ending Balance at Sep. 30, 2018	$ 127,003	19,586,455	(9,397,814)	(57,788,787)				(47,473,143)
Equity, Ending Balance (in shares) at Sep. 30, 2018	1,154,564
Temporary Equity, Beginning Balance at Jun. 30, 2018					$ 6,483,044	$ 49,742,942
Temporary Equity, Beginning Balance (in shares) at Jun. 30, 2018					612,446	7,235,969
Temporary Equity, Ending Balance at Sep. 30, 2018					$ 6,483,044	$ 49,742,942
Temporary Equity, Ending Balance (in shares) at Sep. 30, 2018					612,446	7,235,969
Equity, Beginning Balance at Jun. 30, 2018	$ 127,003	19,506,664	(9,463,614)	(54,650,525)				(44,480,472)
Equity, Beginning Balance (in shares) at Jun. 30, 2018	1,154,564
Increase (Decrease) in Stockholders' Equity
Stock based compensation		79,791						79,791
Foreign currency translation			65,800					65,800
Net loss				(3,138,262)				(3,138,262)
Equity, Ending Balance at Sep. 30, 2018	$ 127,003	19,586,455	(9,397,814)	(57,788,787)				(47,473,143)
Equity, Ending Balance (in shares) at Sep. 30, 2018	1,154,564
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 Series C convertible preferred stock, net of issuance costs of $53,509							$ 5,598,362
Issuance of Series C 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
Temporary Equity, Ending Balance at Sep. 30, 2019					$ 6,483,044	$ 49,742,942	$ 61,963,007
Temporary Equity, Ending Balance (in shares) at Sep. 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
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)				(70,795,660)
Equity, Ending Balance (in shares) at Sep. 30, 2019	1,181,733
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
Temporary Equity, Ending Balance at Sep. 30, 2019					$ 6,483,044	$ 49,742,942	$ 61,963,007
Temporary Equity, Ending Balance (in shares) at Sep. 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 and conversion of preferred stock and common stock of Aprea Therapeutics AB into common 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)				$ (70,795,660)
Equity, Ending Balance (in shares) at Sep. 30, 2019	1,181,733