v3.10.0.1
Document and Entity Information - shares
9 Months Ended
Sep. 30, 2018
Oct. 31, 2018
Entity Information [Line Items]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Sep. 30, 2018  
Document Fiscal Year Focus 2018  
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  
Entity Emerging Growth Company false  
Entity Small Business false  
Class A Common Stock [Member]    
Entity Information [Line Items]    
Entity Common Stock, Shares Outstanding   187,615,732
Class B Convertible Common Stock [Member]    
Entity Information [Line Items]    
Entity Common Stock, Shares Outstanding   34,450,000
Class C Common Stock [Member]    
Entity Information [Line Items]    
Entity Common Stock, Shares Outstanding   226,300,665