Debt Instrument, Associated Derivative Transactions, Receive Amount

No definition available.

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Namespace Prefix:	art_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Number of shares of equity interests issued or issuable to acquire entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)(4)
-URI http://asc.fasb.org/extlink&oid=120321790&loc=d3e6927-128479

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=116859721&loc=d3e6613-128477

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120321790&loc=d3e6927-128479

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=116859721&loc=d3e6578-128477

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Balance Type:	credit
Period Type:	duration

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3255-108585

+ Details

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

- Definition

The number of shares issued or sold by the subsidiary or equity method investee per stock transaction.

+ References

No definition available.

+ Details

Name:	us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Per share amount received by subsidiary or equity investee for each share of common stock issued or sold in the stock transaction.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
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

No definition available.

+ Details

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- Details

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- Details

Name:	us-gaap_DebtInstrumentAxis=art_OnePointSixTwoPercentAndOnePointSixFivePercentSeniorSecuredNotesMember
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- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeForwardMember
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- Details

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- Details

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- Details

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- Details

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Subsequent Events (Details) $ / shares in Units, € in Millions, $ in Millions									1 Months Ended
	Nov. 02, 2020 USD ($)	Oct. 30, 2020 USD ($)	Oct. 30, 2020 EUR (€)	Oct. 15, 2020 $ / shares shares	Oct. 13, 2020 USD ($)	Apr. 22, 2019 $ / shares shares	Sep. 18, 2018 $ / shares shares	Jan. 23, 2018 shares	Mar. 31, 2019 $ / shares shares
Public Offering
Subsequent Event [Line Items]
Number of shares issued (in shares)						42,062,000	4,000,000
Offering price (in USD per share) \| $ / shares						$ 29.75	$ 24.50		$ 27.75
Underwriter's Option
Subsequent Event [Line Items]
Number of shares issued (in shares)						6,562,000		4,350,000	6,063,105
Subsequent Event \| Senior Notes \| Debt Private Placement
Subsequent Event [Line Items]
Debt issued \| €			€ 750
Subsequent Event \| Senior Notes \| Debt Private Placement \| Foreign exchange forwards
Subsequent Event [Line Items]
Debt issued after foreign exchange forward \| $		$ 877
Subsequent Event \| Senior Notes \| 1.62% Debt Private Placement
Subsequent Event [Line Items]
Debt issued \| €			€ 400
Fixed interest rate		1.62%	1.62%
Term of debt		10 years	10 years
Subsequent Event \| Senior Notes \| 1.65% Debt Private Placement
Subsequent Event [Line Items]
Debt issued \| €			€ 350
Fixed interest rate		1.65%	1.65%
Term of debt		12 years	12 years
Subsequent Event \| Public Offering
Subsequent Event [Line Items]
Number of shares issued (in shares)				31,900,000
Offering price (in USD per share) \| $ / shares				$ 36.67
Subsequent Event \| Underwriter's Option
Subsequent Event [Line Items]
Number of shares issued (in shares)				4,785,000
Subsequent Event \| Agro Merchants Group
Subsequent Event [Line Items]
Consideration for acquisition \| $					$ 1,740
Number of shares issued (in shares)				14,166,667
Subsequent Event \| Halls Warehouse Corporation
Subsequent Event [Line Items]
Consideration for acquisition \| $	$ 480