Earnings Per Common Share - Narrative (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Net Income
Basic earnings per share	$ 46,218us-gaap_NetIncomeLoss	$ 83,397us-gaap_NetIncomeLoss
Stock options	0atw_DilutedUndistributedEarningsOptions	0atw_DilutedUndistributedEarningsOptions
Restricted stock and performance units	0	0
Diluted earnings per share	$ 46,218	$ 83,397
Shares
Basic earnings per share (in shares)	64,405,000	64,112,000
Stock options (in shares)	99,000	307,000
Restricted stock (in shares)	511,000	607,000
Diluted earnings per share (in shares)	65,015,000	65,026,000
Per Share Amount
Basic earnings per share (in dollars per share)	$ 0.72us-gaap_EarningsPerShareBasic	$ 1.30us-gaap_EarningsPerShareBasic
Stock options (in dollars per share)	$ 0.00	$ (0.01)
Restricted stock (in dollars per share)	$ (0.01)	$ (0.01)
Diluted earnings per share (in dollars per share)	$ 0.71us-gaap_EarningsPerShareDiluted	$ 1.28us-gaap_EarningsPerShareDiluted
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding stock options, excluded in the calculation of earnings per share	600,000	0

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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