Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2023	Nov. 03, 2023
Document and Entity Information
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2023
Entity File Number	001-40356
Entity Registrant Name	Rain Oncology Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	82-1130967
Entity Address, Address Line One	8000 Jarvis Avenue
Entity Address, Address Line Two	Suite 204
Entity Address, City or Town	Newark
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94560
City Area Code	510
Local Phone Number	953-5559
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	RAIN
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		36,375,671
Entity Central Index Key	0001724979
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Amendment Flag	false