Nature of business and basis of presentation (Details) $ / shares in Units, $ in Millions	1 Months Ended
Sep. 30, 2019 $ / shares	Jun. 30, 2020 USD ($) $ / shares	Dec. 31, 2019 $ / shares
Cash balance \| $		$ 112.9
Common stock, par value	$ 0.001	$ 0.001	$ 0.001
Aprea Therapeutics AB
Common stock, par value	$ 0.11
Convertible preferred stock \| Aprea Therapeutics AB
Conversion ratio	1
Common Stock \| Aprea Therapeutics AB
Conversion ratio	1

Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Excludes cash and cash equivalents within disposal group and discontinued operation.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section 45
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=118262064&loc=SL116631418-115840

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.1)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section 45
-Paragraph 21
-URI http://asc.fasb.org/extlink&oid=118262064&loc=SL116631419-115840

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