SUBSEQUENT EVENTS - Espresso Credit Agreement (Details) - Espresso Credit Agreement - Line of Credit - Subsequent Event $ in Millions	Nov. 02, 2026 USD ($)
Secured Debt
Subsequent Event [Line Items]
Maximum borrowing capacity	$ 983.7
Credit facility, draw period	18 months
Commitment fee percentage	0.40%
Extension term	1 year
Extension option, fee	0.125%
Secured Debt \| Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Subsequent Event [Line Items]
Variable interest rate	1.375%
Secured Debt \| Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate \| Second anniversary
Subsequent Event [Line Items]
Variable interest rate	1.50%
Secured Debt \| Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate \| Three anniversary
Subsequent Event [Line Items]
Variable interest rate	1.625%
Secured Debt \| Adjusted Base Rate
Subsequent Event [Line Items]
Variable interest rate	0.375%
Secured Debt \| Adjusted Base Rate \| Second anniversary
Subsequent Event [Line Items]
Variable interest rate	0.50%
Secured Debt \| Adjusted Base Rate \| Three anniversary
Subsequent Event [Line Items]
Variable interest rate	0.625%
Secured Debt \| Rate Floor
Subsequent Event [Line Items]
Variable interest rate	0.00%
Letter of Credit
Subsequent Event [Line Items]
Maximum borrowing capacity	$ 66.5

Line of Credit Facility, Draw Period, Term

No definition available.

Name:	aci_LineOfCreditFacilityDrawPeriodTerm
Namespace Prefix:	aci_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Line Of Credit Facility, Extension Option, Fee, Percentage

+ References

No definition available.

+ Details

Name:	aci_LineOfCreditFacilityExtensionOptionFeePercentage
Namespace Prefix:	aci_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line Of Credit Facility, Extension Term

+ References

No definition available.

+ Details

Name:	aci_LineOfCreditFacilityExtensionTerm
Namespace Prefix:	aci_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480657/210-10-S50-8

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(19)(b))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 830
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481674/830-30-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 855
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483399/855-10-50-2

+ Details

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

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_SecuredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=aci_EspressoCreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	aci_VariableRateStepUpPeriodAxis=aci_VariableRateStepUpPeriodOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	aci_VariableRateStepUpPeriodAxis=aci_VariableRateStepUpPeriodTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=aci_AdjustedBaseRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=aci_RateFloorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_LetterOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: