v3.8.0.1
Document and Entity Information - shares
9 Months Ended
Sep. 30, 2017
Oct. 31, 2017
Entity Information [Line Items]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Sep. 30, 2017  
Document Fiscal Year Focus 2017  
Document Fiscal Period Focus Q3  
Trading Symbol UA  
Entity Registrant Name UNDER ARMOUR, INC.  
Entity Central Index Key 0001336917  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Class A Common Stock [Member]    
Entity Information [Line Items]    
Entity Common Stock, Shares Outstanding   185,130,747
Class B Convertible Common Stock [Member]    
Entity Information [Line Items]    
Entity Common Stock, Shares Outstanding   34,450,000
Common Class C [Member]    
Entity Information [Line Items]    
Entity Common Stock, Shares Outstanding   222,117,109