| Cover | Oct. 30, 2020 | Feb. 11, 2020 |
| Entity Information [Line Items] | ||
| Document Type | 8-K | |
| Document Period End Date | Oct. 30, 2020 | |
| 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 | |
| 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 |
