LOANS RECEIVABLE - Loans Modification (Details) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2022 USD ($) contract	Dec. 31, 2021 USD ($) loan contract
Financing Receivable, Allowance for Credit Loss [Line Items]
Number of contracts \| contract	0	3
Pre-modification Outstanding Recorded Investment		$ 186
Post-modification Outstanding Recorded Investment		$ 189
TDR modified maturity term	3 months
Number of payment defaults \| loan		3
Commitment to lend additional fund	$ 0	$ 0
One- to four-family residential
Financing Receivable, Allowance for Credit Loss [Line Items]
Number of contracts \| contract		3
Pre-modification Outstanding Recorded Investment		$ 186
Post-modification Outstanding Recorded Investment		$ 189

The amount of commitments to lend additional funds to existing TDR relationships.

No definition available.

Name:	clst_FinancingReceivableModificationsCommitmentsToLendAdditionalFundsToExistingTroubleDebtRestructurings
Namespace Prefix:	clst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Troubled debt restructured loans modified average maturity term.

+ References

No definition available.

+ Details

Name:	clst_TroubledDebtRestructuredLoansModificationAverageMaturityTerm
Namespace Prefix:	clst_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after troubled debt restructuring, of modified financing receivable.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount, before troubled debt restructuring, of financing receivable to be modified.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Number of financing receivable contracts modified as troubled debt restructuring within previous 12 months, with subsequent payment default.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953682-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=clst_OneToFourFamilyResidentialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: