| Document and Entity Information | Nov. 06, 2019 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001157601 |
| Document Type | 8-K |
| Document Period End Date | Nov. 6, 2019 |
| Entity Registrant Name | MADRIGAL PHARMACEUTICALS, INC. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-33277 |
| Entity Tax Identification Number | 04-3508648 |
| Entity Address, Address Line One | Four Tower Bridge |
| Entity Address, Address Line Two | 200 Barr Harbor Drive |
| Entity Address, Address Line Three | Suite 200 |
| Entity Address, City or Town | West Conshohocken |
| Entity Address, State or Province | PA |
| Entity Address, Postal Zip Code | 19428 |
| City Area Code | (267) |
| Local Phone Number | 824-2827 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, $0.0001 Par Value Per Share |
| Trading Symbol | MDGL |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
