Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2020	May 01, 2020
Document and Entity Information [Abstract]
Entity Registrant Name	Jounce Therapeutics, Inc.
Entity Central Index Key	0001640455
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Small Business	true
Document Type	10-Q
Document Period End Date	Mar. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		34,053,091
Entity Shell Company	false
Entity Current Reporting Status	Yes