Document and Entity Information
9 Months Ended
Sep. 30, 2014
Nov. 04, 2014
Document and Entity Information    
Entity Registrant Name Karyopharm Therapeutics Inc.  
Entity Central Index Key 0001503802  
Document Type 10-Q  
Document Period End Date Sep. 30, 2014  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Entity Current Reporting Status Yes  
Entity Filer Category Non-accelerated Filer  
Entity Common Stock, Shares Outstanding   32,700,563
Document Fiscal Year Focus 2014  
Document Fiscal Period Focus Q3