Property And Equipment (Narrative) (Details) (USD $)	9 Months Ended
Jun. 30, 2011
Number of drilling units	5
Expenditure on construction of drilling units in progress	$ 645,000,000
Commitments on drilling units under construction	$ 1,200,000,000
Atwood Osprey [Member]
Number of drilling units	1
Atwood Condor [Member]
Number of drilling units	1
Atwood Mako [Member]
Number of drilling units	1
Atwood Manta [Member]
Number of drilling units	1
Atwood Orca [Member]
Number of drilling units	1
Atwood Advantage [Member]
Number of drilling units	1

Gross amount, at the balance sheet date, of long-lived assets under construction that include construction costs to date on capital projects that have not been completed and assets being constructed that are not ready to be placed into service.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Principles Board Opinion (APB)
-Number 12
-Paragraph 5
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Name:	us-gaap_ConstructionInProgressGross
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant