| Cover | Feb. 09, 2021 |
| Entity Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | Feb. 9, 2021 |
| Entity Registrant Name | UNDER ARMOUR, INC. |
| Entity Incorporation, State or 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 |
| Amendment Flag | false |
| Entity Central Index Key | 0001336917 |
| Current Fiscal Year End Date | --12-31 |
| Class A Common Stock | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | Class A Common Stock |
| Trading Symbol | UAA |
| Security Exchange Name | NYSE |
| Class C Common Stock | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | Class C Common Stock |
| Trading Symbol | UA |
| Security Exchange Name | NYSE |
