Cover Page - USD ($) $ in Billions	12 Months Ended
	Apr. 30, 2020	Jun. 09, 2020	Oct. 31, 2019
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Apr. 30, 2020
Document Transition Report	false
Entity File Number	001-34700
Entity Registrant Name	CASEY’S GENERAL STORES, INC.
Entity Incorporation, State or Country Code	IA
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
Title of 12(b) Security	Common Stock, no par value per share
Trading Symbol	CASY
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth	false
Entity Shell Company	false
Entity Public Float			$ 6.3
Entity Common Stock, Shares Outstanding		36,849,324
Entity Central Index Key	0000726958
Amendment Flag	false
Current Fiscal Year End Date	--04-30
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY