v3.8.0.1
Document and Entity Information - shares
9 Months Ended
Sep. 30, 2017
Oct. 31, 2017
Document and Entity Information    
Entity Registrant Name Loxo Oncology, Inc.  
Entity Central Index Key 0001581720  
Document Type 10-Q  
Document Period End Date Sep. 30, 2017  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Entity Current Reporting Status Yes  
Entity Filer Category Accelerated Filer  
Entity Common Stock, Shares Outstanding   29,937,504
Document Fiscal Year Focus 2017  
Document Fiscal Period Focus Q3