Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2022	Aug. 10, 2022
Document and Entity Information
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Jun. 30, 2022
Entity File Number	001-37990
Entity Address, Address Line One	47 Thorndike St, Suite B1-1
Entity Address, City or Town	Cambridge
Entity Address, Postal Zip Code	02141
Entity Address, State or Province	MA
Entity Incorporation, State or Country Code	DE
City Area Code	617
Local Phone Number	714-0360
Entity Tax Identification Number	27-4412575
Entity Registrant Name	LEAP THERAPEUTICS, INC.
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	LPTX
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		99,021,376
Entity Central Index Key	0001509745
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q2
Amendment Flag	false