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Cover Page - shares
 6 Months Ended
Jun. 30, 2021
Jul. 26, 2021
Cover [Abstract]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Jun. 30, 2021  
Document Transition Report false  
Entity File Number 001-36112  
Entity Registrant Name MACROGENICS, INC.  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 06-1591613  
Entity Address, Address Line One 9704 Medical Center Drive  
Entity Address, City or Town Rockville  
Entity Address, State or Province MD  
Entity Address, Postal Zip Code 20850  
City Area Code 301  
Local Phone Number 251-5172  
Title of 12(b) Security Common Stock, par value $0.01 per share  
Trading Symbol MGNX  
Security Exchange Name NASDAQ  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   61,107,288
Amendment Flag false  
Document Fiscal Year Focus 2021  
Document Fiscal Period Focus Q2  
Entity Central Index Key 0001125345  
Current Fiscal Year End Date --12-31