Long-term Debt and Fair Value Disclosure (Details) - USD ($)	3 Months Ended
Jul. 31, 2019	Apr. 30, 2019
Debt Instrument
Fair value of long-term debt	$ 1,323,000,000	$ 1,272,000,000
Unsecured Revolving Credit Facility Due January 2024 \| Revolving Credit Facility
Debt Instrument
Maximum borrowing capacity	300,000,000
Fair value of amount outstanding	50,000,000	75,000,000
Unsecured Revolving Credit Facility Due January 2024 \| Revolving Credit Facility \| Letter of Credit
Debt Instrument
Maximum borrowing capacity	30,000,000
Unsecured Revolving Credit Facility Due January 2024 \| Revolving Credit Facility \| Swingline Loans
Debt Instrument
Maximum borrowing capacity	$ 30,000,000
Unsecured Revolving Credit Facility Due January 2024 \| Minimum \| Revolving Credit Facility
Debt Instrument
Facility fee percentage	0.20%
Unsecured Revolving Credit Facility Due January 2024 \| Maximum \| Revolving Credit Facility
Debt Instrument
Facility fee percentage	0.40%
Unsecured Revolving Line of Credit \| Line of Credit
Debt Instrument
Maximum borrowing capacity	$ 25,000,000
Fair value of amount outstanding	$ 0	$ 0

Line Of Credit Facility, Facility Fee Percentage

No definition available.

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Namespace Prefix:	casy_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value of the amount outstanding under the credit facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13433-108611

+ Details

Name:	us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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