COMMITMENTS AND CONTINGENCIES (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
COMMITMENTS AND CONTINGENCIES.
Commitments to originate loans	$ 120	$ 11,979
Undisbursed portion of construction loans in process	10,525	7,635
Unused lines of credit	16,385	15,391
Unused overdraft privilege amounts	1,220	1,167
Letters of credit		19
Total	$ 28,250	$ 36,191

The amount of commitments to originate loans with off-balance-sheet risk.

No definition available.

Name:	clst_CommitmentsToExtendCredit
Namespace Prefix:	clst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of financial instruments with off-balance-sheet risk.

No definition available.

Name:	clst_FinancialInstrumentsOffBalanceSheetRisk
Namespace Prefix:	clst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of letters of credit with off-balance-sheet risk.

No definition available.

Name:	clst_FinancialInstrumentsWithOffBalanceSheetRiskLettersOfCredit
Namespace Prefix:	clst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of unused lines of credit with off-balance-sheet risk.

No definition available.

Name:	clst_FinancialInstrumentsWithOffBalanceSheetRiskUnusedLinesOfCredit
Namespace Prefix:	clst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

The amounts of unused overdraft privilege with off-balance-sheet risk.

No definition available.

Name:	clst_OverdraftPrivilegeUnusedAmounts
Namespace Prefix:	clst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

The amount of unfunded financial commitments with off-balance-sheet risk.

No definition available.

Name:	clst_UnfundedConstructionLoansInProcess
Namespace Prefix:	clst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

No definition available.

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