| Document and Entity Information | Jan. 31, 2021 |
| Cover [Abstract] | |
| Entity Registrant Name | Horizon Therapeutics Public Ltd Co |
| Entity Tax Identification Number | 00-0000000 |
| Amendment Flag | false |
| Entity Central Index Key | 0001492426 |
| Document Type | 8-K |
| Document Period End Date | Jan. 31, 2021 |
| Entity Incorporation State Country Code | L2 |
| Entity File Number | 001-35238 |
| Entity Address, Address Line One | Connaught House |
| Entity Address, Address Line Two | 1st Floor |
| Entity Address, Address Line Three | 1 Burlington Road |
| Entity Address, City or Town | Dublin 4 |
| Entity Address, Postal Zip Code | D04 C5Y6 |
| Entity Address, Country | IE |
| City Area Code | 011-353-1 |
| Local Phone Number | 772-2100 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | true |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Ordinary shares, nominal value $0.0001 per share |
| Trading Symbol | HZNP |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
