FAIR VALUE OF FINANCIAL INSTRUMENTS - Narrative (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Sep. 30, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Credit valuation adjustment to total fair value percentage (less than)	1.00%
Senior Notes \| 6.5% Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Long-term debt, carrying value	$ 451,200
Principal amount	448,650	$ 448,650
Long-term debt, fair value	$ 439,300

Fair Value Input, Credit Valuation Adjustment to Total Fair Value Percentage

No definition available.

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- Definition

Long Term Debt, Amount After (Discount) Premium, Before Debt Issuance Costs

+ References

No definition available.

+ Details

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Namespace Prefix:	atw_
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Balance Type:	credit
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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

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- 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

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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- Details

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