Property and Equipment (Narrative) (Details) (USD $)	3 Months Ended	6 Months Ended
Mar. 31, 2013 DrillingUnits	Mar. 31, 2012	Mar. 31, 2013 DrillingUnits	Mar. 31, 2012
Property, Plant and Equipment [Abstract]
Interest capitalized	$ 6,500,000	$ 9,600,000	$ 15,600,000	$ 16,000,000
Expenditure towards construction of drilling units currently under construction	590,000,000		590,000,000
Number of drilling units	4		4
Number of drilling units with upaid firm commitments	4		4
Commitments on drilling units under construction			$ 1,100,000,000

Amount of interest capitalized, including amount of allowance for funds used during construction.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 34

-Paragraph 21

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

-Glossary Allowance for Funds Used during Construction

-URI http://asc.fasb.org/extlink&oid=6504829

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 835

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6501662&loc=d3e56162-110433

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration