| Cover Page | Dec. 02, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Dec. 2, 2020 |
| Entity Registrant Name | CASEY'S GENERAL STORES, INC. |
| Entity Incorporation, State or Country Code | IA |
| Entity File Number | 001-34700 |
| Entity Tax Identification Number | 42-0935283 |
| Entity Address, Address Line One | One SE Convenience Blvd. |
| Entity Address, City or Town | Ankeny |
| Entity Address, State or Province | IA |
| Entity Address, Postal Zip Code | 50021 |
| City Area Code | 515 |
| Local Phone Number | 965-6100 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, no par value per share |
| Trading Symbol | CASY |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0000726958 |
| Amendment Flag | false |
| Current Fiscal Year End Date | --04-30 |
