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Long-Term Debt - Summary of Long-Term Debt (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Sep. 30, 2014
Debt Instrument [Line Items]    
Stated interest rate 1.57%us-gaap_DebtInstrumentInterestRateStatedPercentage  
Long-term Debt $ 1,741,834us-gaap_LongTermDebt $ 1,742,122us-gaap_LongTermDebt
Senior Notes | 6.5% Senior Notes    
Debt Instrument [Line Items]    
Stated interest rate 6.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= atw_SixPointFivePercentSeniorNotesMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember		 6.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= atw_SixPointFivePercentSeniorNotesMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
Long-term Debt 656,834us-gaap_LongTermDebt
/ us-gaap_DebtInstrumentAxis
= atw_SixPointFivePercentSeniorNotesMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember		 657,122us-gaap_LongTermDebt
/ us-gaap_DebtInstrumentAxis
= atw_SixPointFivePercentSeniorNotesMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
Revolving Credit Facility    
Debt Instrument [Line Items]    
Long-term Debt $ 1,085,000us-gaap_LongTermDebt
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_RevolvingCreditFacilityMember		 $ 1,085,000us-gaap_LongTermDebt
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_RevolvingCreditFacilityMember