Defined Benefit Plan, Average Future Service Period

No definition available.

Name:	art_DefinedBenefitPlanAverageFutureServicePeriod
Namespace Prefix:	art_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Defined Benefit Plans, Number of Plans

+ References

No definition available.

+ Details

Name:	art_DefinedBenefitPlansNumberOfPlans
Namespace Prefix:	art_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Government Sponsored Plans, Contributions

+ References

No definition available.

+ Details

Name:	art_GovernmentSponsoredPlansContributions
Namespace Prefix:	art_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Multiemployer Plan, Collective-Bargaining Arrangement, Percentage of Employer's Collective-Bargaining Participants Covered

+ References

No definition available.

+ Details

Name:	art_MultiemployerPlanCollectiveBargainingArrangementPercentageofEmployersCollectiveBargainingParticipantsCovered
Namespace Prefix:	art_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480482/715-20-55-17

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 3A
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480535/715-20-45-3A

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 18
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480482/715-20-55-18

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (h)(5)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)(5)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-6

+ Details

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

- Definition

Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (j)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-5

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-8

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

+ Details

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

- Definition

Amount of payment, which decreases benefit obligation of defined benefit plan, for irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Transaction constituting settlement includes, but is not limited to, making lump-sum cash payment to participant in exchange for their rights to receive specified benefits and purchasing nonparticipating annuity contract. Excludes decreases to benefit obligation for remeasurement due to settlement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)(10)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

+ Details

Name:	us-gaap_DefinedBenefitPlanBenefitObligationPaymentForSettlement
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of increase (decrease) in benefit obligation of defined benefit plan from change, classified as other.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedBenefitPlanOtherChanges
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

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

- Definition

Amount of cost for defined contribution plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 70
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480794/715-70-50-1

+ Details

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

- Definition

Amount of cost for employer contribution required to be made in future period to multiemployer pension plan determined to be individually significant. Includes, but is not limited to, employer contribution required by collective-bargaining arrangement (CBA), statutory obligation, and other contractual obligation.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 80
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (f)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480576/715-80-50-5

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 715
-SubTopic 80
-Name Accounting Standards Codification
-Section 55
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480547/715-80-55-8

+ Details

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

- Details

Name:	us-gaap_RetirementPlanTypeAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanSponsorLocationAxis=country_US
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementScenarioAxis=srt_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanSponsorLocationAxis=country_AU
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanNameAxis=art_AustriaPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanSponsorLocationAxis=us-gaap_ForeignPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanNameAxis=art_SuperannuationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Employee Benefit Plans - Narrative (Details) $ in Millions		12 Months Ended
Employee Benefit Plans - Narrative (Details) $ in Millions	Nov. 27, 2023 USD ($)	Dec. 31, 2026 USD ($)	Dec. 31, 2025 USD ($) plan	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Cash annuity payment	$ 1.3
Recognition of a settlement loss					$ 2.5
Total plan assets allocated			94.00%
Percentage of union employees covered			34.00%
Minimum contribution to multiemployer plan			$ 3.6
Contributions to government sponsored plan			10.0	$ 9.1	8.3
Defined contribution plan expense			$ 12.2	$ 11.8	$ 11.9
Other Post-Retirement Benefits (OPRB)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Average future service period			3 years 3 months 18 days
North America \| Forecast
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amortization of net periodic benefit cost (less than)		$ 0.1
Australia \| Forecast
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amortization of net periodic benefit cost (less than)		$ 0.1
Austria Plans \| Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Average future service period			4 years
Austria Plans \| Foreign Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of plans \| plan			2
Superannuation \| Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Average future service period			5 years
Expected return on plan assets			7.50%	7.50%	5.00%
Superannuation \| Pension \| Forecast
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets		7.30%