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Employee Benefit and Stock Compensation Plans Expected Fututre Annuity Payments (Details) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Mar. 31, 2022 | Mar. 31, 2018 | Mar. 31, 2017 | Mar. 31, 2016 | Mar. 31, 2015 | Mar. 31, 2014 | Mar. 31, 2013
Expected future annuity payments [Line Items] |  |  |  |  |  |  |
Expected Future Annuity Payments | $ 720 | $ 156 | $ 162 | $ 155 | $ 161 | $ 166 |
Total Annuity Payments |  |  |  |  |  |  | $ 1,520

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- Definition Expected Future Annuity Payments + References No definition available. + Details
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Period Type: | duration

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- Details
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- Definition Total Annuity Payments + References No definition available. + Details
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Namespace Prefix: | carv_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration