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Acquisitions (Details) | 12 Months Ended
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Apr. 30, 2016 store
Business Combinations [Abstract] |
Number of stores acquired | 5
Number of stores opened | 4
Number of stores expected to open in next fiscal year | 1
Goodwill deductible for income tax purposes period (in years) | 15 years

X
- Definition Goodwill deductible for income tax purposes, period. + References No definition available. + Details
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Namespace Prefix: | casy_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Number of stores expected to open in next fiscal year. + References No definition available. + Details
Name: | casy_NumberOfStoresExpectedToOpenInNextFiscalYear
Namespace Prefix: | casy_
Data Type: | xbrli:positiveIntegerItemType
Balance Type: | na
Period Type: | duration

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- Definition Number of stores opened in the period. + References No definition available. + Details
Name: | casy_NumberOfStoresOpened
Namespace Prefix: | casy_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The number of businesses acquired by the entity during the period. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration