Cover Page - shares	3 Months Ended
	Mar. 31, 2020	Apr. 30, 2020
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2020
Document Transition Report	false
Entity File Number	001-33202
Entity Registrant Name	UNDER ARMOUR, INC.
Entity Incorporation, State or Country Code	MD
Entity Tax Identification Number	52-1990078
Entity Address, Address Line One	1020 Hull Street
Entity Address, City or Town	Baltimore
Entity Address, State or Province	MD
Entity Address, Postal Zip Code	21230
City Area Code	410
Local Phone Number	454-6428
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Entity Central Index Key	0001336917
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Class A Common Stock [Member]
Document Information [Line Items]
Title of 12(b) Security	Class A Common Stock
Trading Symbol	UAA
Security Exchange Name	NYSE
Entity Common Stock, Shares Outstanding		188,452,489
Class B Convertible Common Stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		34,450,000
Class C Common Stock [Member]
Document Information [Line Items]
Title of 12(b) Security	Class C Common Stock
Trading Symbol	UA
Security Exchange Name	NYSE
Entity Common Stock, Shares Outstanding		231,191,334