| Document and Entity Information | Oct. 28, 2020 |
| Document And Entity Information [Line Items] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001336917 |
| Document Type | 8-K |
| Document Period End Date | Oct. 28, 2020 |
| Entity Registrant Name | UNDER ARMOUR, INC. |
| Entity Incorporation State Country Code | MD |
| Entity File Number | 001-33202 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Common Stock [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Class A Common Stock |
| Trading Symbol | UAA |
| Security Exchange Name | NYSE |
| Common Class C [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Class C Common Stock |
| Trading Symbol | UA |
| Security Exchange Name | NYSE |
