v3.8.0.1
Document and Entity Information - USD ($)
$ in Billions
12 Months Ended
Dec. 31, 2017
Feb. 23, 2018
Jun. 30, 2017
Document and Entity Information      
Entity Registrant Name Loxo Oncology, Inc.    
Entity Central Index Key 0001581720    
Document Type 10-K    
Document Period End Date Dec. 31, 2017    
Amendment Flag false    
Current Fiscal Year End Date --12-31    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Filer Category Large Accelerated Filer    
Entity Public Float     $ 1.4
Entity Common Stock, Shares Outstanding   30,034,173  
Document Fiscal Year Focus 2017    
Document Fiscal Period Focus FY