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FAIR VALUE MEASUREMENTS - Narratives (Details) - USD ($) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024 | Dec. 31, 2024
FAIR VALUE MEASUREMENTS |  |  |  |  |
Impaired loans, carrying amount | $ 214,000 |  | $ 214,000 |  | $ 452,000
Net loss to adjust foreclosed assets to fair value | $ 4,000 | $ 39,000 | $ 18,000 | $ 37,000 |

X
- Definition Amount of increase (decrease) in the fair value of foreclosed assets recognized in the income statement. + References No definition available. + Details
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Namespace Prefix: | clst_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Carrying amount of impaired loans. + References No definition available. + Details
Name: | clst_ImpairedLoanCarryingAmount
Namespace Prefix: | clst_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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