Nature of business and basis of presentation (Details) $ / shares in Units, $ in Millions	1 Months Ended
	Sep. 30, 2019 $ / shares	Mar. 31, 2021 USD ($) $ / shares	Dec. 31, 2020 $ / shares
Cash balance | $		$ 77.6
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001	$ 0.001
Aprea Therapeutics AB
Common stock, par value (in dollars per share)	$ 0.11
Convertible preferred stock | Aprea Therapeutics AB
Conversion ratio	1
Common Stock | Aprea Therapeutics AB
Conversion ratio	1