v3.8.0.1
Document and Entity Information - shares
3 Months Ended
Mar. 31, 2018
Apr. 30, 2018
Entity Information [Line Items]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Mar. 31, 2018  
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q1  
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   185,977,014
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   224,224,628