Debt Instrument, Collateral Number of Properties

No definition available.

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- Definition

Debt Instrument, Covenant, Borrowing Base Debt Service Coverage Ratio, Minimum

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Covenant, Fixed Charge Coverage Ratio, Minimum

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Covenant, Leverage Ratio After Material Acquisition, Maximum

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Debt Instrument, Covenant, Leverage Ratio, Maximum

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Debt Instrument, Covenant, Material Acquisition Threshold

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Debt Instrument, Covenant, Principal Repayment if Change in Control Occurs, Percentage

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Debt Instrument, Covenant, Secured Leverage Ratio After Material Acquisition, Maximum

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Covenant, Secured Leverage Ratio, Maximum

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Debt Instrument, Covenant, Unencumbered Leverage Ratio After Material Acquisition, Maximum

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Debt Instrument, Covenant, Unencumbered Leverage Ratio, Maximum

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Covenant, Unsecured Debt Service Ratio, Minimum

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Covenant, Unsecured Interest Coverage Ratio, Minimum

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Extension Fee

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Debt Instrument, Increase (Decrease) on Basis Spread on Variable Rate Basis

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Debt Instrument, Maximum Borrowing Capacity

+ References

No definition available.

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Debt Instrument, Minimum Principal for Early Repayment of Debt

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Notice Period for Early Repayment of Debt

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Number of Instruments

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Debt Instrument, Number of Tranches

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Line of Credit, Commitment Fee Increase (Decrease), Percentage

+ References

No definition available.

+ Details

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

- Definition

Line of Credit, Commitment Fee Increase (Decrease), Threshold, Percentage

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Line of Credit Facility, Extension Term

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Line of Credit Facility, Maximum Borrowing Capacity Available to be Used for Foreign Currencies

+ References

No definition available.

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Line of Credit Facility, Number of Extensions

+ References

No definition available.

+ Details

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Namespace Prefix:	art_
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Balance Type:	na
Period Type:	instant

- Definition

Number of Real Estate Properties Acquired During Period

+ References

No definition available.

+ Details

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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

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

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
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-SubTopic 30
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+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

+ Details

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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

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- Definition

Value of input used to measure debt instrument, including, but not limited to, convertible and non-convertible debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
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+ Details

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- 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

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- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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-Subparagraph (SX 210.5-02.17)
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Balance Type:	debit
Period Type:	instant

- Definition

The designation of funds furnished by a borrower to a lender to assure future payments of the borrower's real estate taxes and insurance obligations with respect to a mortgaged property. Escrow deposits may be made for a variety of other purposes such as earnest money and contingent payments. This element excludes replacement reserves which are an escrow separately provided for within the US GAAP taxonomy.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Section S99
-Paragraph 1
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+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
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-Paragraph 15
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Debt - Additional Information (Details)								3 Months Ended			9 Months Ended
Debt - Additional Information (Details)	Mar. 26, 2020 USD ($) extension tranche	Sep. 24, 2019	Sep. 23, 2019	Dec. 04, 2018 USD ($)	Dec. 03, 2018 USD ($)	Nov. 06, 2018 USD ($)	May 01, 2013 USD ($) instrument warehouse	Sep. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 CAD ($)	Mar. 26, 2020 CAD ($) extension tranche	Dec. 31, 2019 USD ($)	Apr. 26, 2019 USD ($)
Debt Instrument [Line Items]
Loss on debt extinguishment and modifications								$ 0	$ 800,000	$ 0	$ 781,000	$ 0
Term Loans \| Total 2020 Senior Unsecured Term Loan A Facility
Debt Instrument [Line Items]
Term of debt	5 years
Number of tranches \| tranche	2													2
Unamortized debt issuance cost	$ 3,200,000							7,400,000			$ 7,400,000
Term Loans \| 2020 Senior Unsecured Term Loan Tranche A-1
Debt Instrument [Line Items]
Face amount of debt	425,000,000.0
Term Loans \| 2020 Senior Unsecured Term Loan Tranche A-2
Debt Instrument [Line Items]
Face amount of debt													$ 250,000,000.0	$ 250,000,000.0
Term Loans \| 2018 Senior Unsecured Term Loan A Facility
Debt Instrument [Line Items]
Face amount of debt	$ 475,000,000
Term Loans \| LIBOR \| 2020 Senior Unsecured Term Loan Tranche A-1
Debt Instrument [Line Items]
Applicable interest rate											0.95%
Term Loans \| LIBOR \| 2018 Senior Unsecured Term Loan A Facility
Debt Instrument [Line Items]
Applicable interest rate											1.00%
Line of Credit \| Revolving Credit Facility
Debt Instrument [Line Items]
Unamortized debt issuance cost								6,300,000			$ 6,300,000				$ 2,800,000
Letter of credit amount outstanding								$ 21,000,000.0			$ 21,000,000.0				23,000,000.0
Line of Credit \| Revolving Credit Facility \| 2020 Senior Unsecured Revolving Credit Facility
Debt Instrument [Line Items]
Term of debt	4 years
Revolver borrowing capacity	$ 800,000,000
Unamortized debt issuance cost	$ 5,200,000
Number of extensions \| extension	2													2
Extension term	6 months
Extension fee	0.0625%													0.0625%
Line of Credit \| Revolving Credit Facility \| 2018 Senior Unsecured Revolving Credit Facility
Debt Instrument [Line Items]
Revolver borrowing capacity	$ 800,000,000			$ 800,000,000.0	$ 450,000,000.0
Letter of credit amount outstanding															23,000,000.0
Revolver borrowing capacity, foreign currencies				$ 400,000,000
Fee on unused borrowing capacity		0.20%
Line of Credit \| Revolving Credit Facility \| 2018 Senior Unsecured Term Loan A Facility
Debt Instrument [Line Items]
Change in applicable interest rate				(0.05%)
Unamortized debt issuance cost				$ 8,900,000											$ 6,100,000
Threshold for fee on unused borrowing capacity		50.00%
Line of Credit \| Revolving Credit Facility \| 2020 Senior Unsecured Term Loan A Facility and Senior Unsecured Credit Facility
Debt Instrument [Line Items]
Change in applicable interest rate	(0.05%)
Line of Credit \| Revolving Credit Facility \| LIBOR \| 2020 Senior Unsecured Revolving Credit Facility
Debt Instrument [Line Items]
Applicable interest rate											0.85%
Line of Credit \| Revolving Credit Facility \| LIBOR \| 2018 Senior Unsecured Revolving Credit Facility
Debt Instrument [Line Items]
Applicable interest rate											0.90%
Line of Credit \| Revolving Credit Facility \| LIBOR \| 2018 Senior Unsecured Term Loan A Facility
Debt Instrument [Line Items]
Applicable interest rate		1.00%	1.45%	1.45%	2.35%
Line of Credit and Term Notes \| 2020 Senior Unsecured Term Loan A Facility and Senior Unsecured Credit Facility
Debt Instrument [Line Items]
Total borrowing capacity	$ 1,400,000,000
Maximum leverage ratio	60.00%													60.00%
Maximum leverage ratio after material acquisition	65.00%													65.00%
Maximum unencumbered leverage ratio	60.00%													60.00%
Minimum unencumbered leverage ratio after material acquisition	65.00%													65.00%
Maximum secured leverage ratio	40.00%													40.00%
Maximum secured leverage ratio after material acquisition	45.00%													45.00%
Minimum fixed charge coverage ratio	1.50													1.50
Minimum unsecured interest coverage ratio	1.75													1.75
Material acquisition threshold	5.00%													5.00%
Senior Notes \| Senior Unsecured Notes
Debt Instrument [Line Items]
Maximum leverage ratio						60.00%
Maximum unencumbered leverage ratio						60.00%
Maximum secured leverage ratio						40.00%
Minimum fixed charge coverage ratio						1.50
Minimum principal for repayment of debt						5.00%
Notice period for repayment of debt						10 days
Principal repayment if change in control occurs						100.00%
Minimum unsecured debt service ratio						2.00
Senior Notes \| Series C 4.10% notes due 2030
Debt Instrument [Line Items]
Face amount of debt																$ 350,000,000.0
Fixed interest rate								4.10%			4.10%		4.10%			4.10%
Senior Notes \| Series A 4.68% notes due 2026
Debt Instrument [Line Items]
Face amount of debt						$ 200,000,000.0
Fixed interest rate						4.68%		4.68%			4.68%		4.68%
Senior Notes \| Series B 4.86% notes due 2029
Debt Instrument [Line Items]
Face amount of debt						$ 400,000,000.0
Fixed interest rate						4.86%		4.86%			4.86%		4.86%
Senior Notes \| Discount Rate \| Senior Unsecured Notes \| Valuation Technique, Discounted Cash Flow
Debt Instrument [Line Items]
Discount rate						0.0050
Mortgage Loans \| 2010 CMBS Financing
Debt Instrument [Line Items]
Indebtedness repaid						$ 600,000,000.0
Mortgage Loans \| 2013 Mortgage Loans
Debt Instrument [Line Items]
Face amount of debt							$ 322,000,000.0
Number of properties \| warehouse							15
Restricted cash associated with debt								$ 4,000,000.0			$ 4,000,000.0
Minimum borrowing base debt service coverage ratio							1.10
Mezzanine Notes \| 2013 Mortgage Loans
Debt Instrument [Line Items]
Number of notes \| instrument							2
Number of warehouses acquired \| warehouse							2
Minimum \| Line of Credit \| Revolving Credit Facility \| 2018 Senior Unsecured Revolving Credit Facility
Debt Instrument [Line Items]
Change in fee on unused borrowing capacity		0.05%
Minimum \| Mortgage Loans \| 2013 Mortgage Loans
Debt Instrument [Line Items]
Fixed interest rate							3.81%
Maximum \| Line of Credit \| Revolving Credit Facility \| 2018 Senior Unsecured Revolving Credit Facility
Debt Instrument [Line Items]
Change in fee on unused borrowing capacity		0.15%
Maximum \| Mortgage Loans \| 2013 Mortgage Loans
Debt Instrument [Line Items]
Fixed interest rate							11.50%