Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Feb. 21, 2018	Jun. 30, 2017
Document and Entity Information
Entity Registrant Name	LEAP THERAPEUTICS, INC.
Entity Central Index Key	0001509745
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Public Float			$ 21.5
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Smaller Reporting Company
Entity Common Stock, Shares Outstanding		12,354,014
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY