| Document and Entity Information | Feb. 28, 2020 |
| Document and Entity Information [Abstract] | |
| Entity Central Index Key | 0000019411 |
| Document Type | 8-K |
| Document Period End Date | Feb. 28, 2020 |
| Entity File Number | 1-6639 |
| Entity Registrant Name | MAGELLAN HEALTH INC |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identificatoin Number | 58-1076937 |
| Entity Address, Address Line One | 4801 E. Washington Street |
| Entity Address, City or Town | Phoenix |
| Entity Address, State or Province | AZ |
| Entity Address, Postal Zip Code | 85034 |
| City Area Code | 800 |
| Local Phone Number | 642-1716 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | MGLN |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Amendment Flag | false |
