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v3.20.2

Fair Value Measurements Text Tag (Details) | 3 Months Ended |
--- | --- | ---
Jun. 30, 2020 | Mar. 31, 2020
Fair Value Disclosures [Abstract] |  |
Percent of Total Assets Level 3 | 0.02% | 0.03%
Transfers between level 1 and level 2 | 0 |

X
- Definition Percent of Total Assets Level 3 + References No definition available. + Details
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Namespace Prefix: | carv_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Transfers between level 1 and level 2 + References No definition available. + Details
Name: | carv_Transfersbetweenlevel1andlevel2
Namespace Prefix: | carv_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | duration

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