Financial Instruments and Fair Value Disclosures (Details) (USD $)	Jun. 30, 2011	Dec. 31, 2010
5.15% Senior Notes (due 2014) [Member]
Fair values and related carrying values of our debt instruments
Senior notes	$ 249,778,000	$ 249,745,000
Interest rate of senior notes	5.15%
5.15% Senior Notes (due 2014) [Member] \| Carrying Value [Member]
Fair values and related carrying values of our debt instruments
Senior notes	249,800,000	249,700,000
5.15% Senior Notes (due 2014) [Member] \| Fair Value [Member]
Fair values and related carrying values of our debt instruments
Debt Instrument, Fair Value	274,000,000	271,100,000
4.875% Senior Notes (due 2015) [Member]
Fair values and related carrying values of our debt instruments
Senior notes	249,751,000	249,724,000
Interest rate of senior notes	4.875%
4.875% Senior Notes (due 2015) [Member] \| Carrying Value [Member]
Fair values and related carrying values of our debt instruments
Senior notes	249,700,000	249,700,000
4.875% Senior Notes (due 2015) [Member] \| Fair Value [Member]
Fair values and related carrying values of our debt instruments
Debt Instrument, Fair Value	271,100,000	270,000,000
5.875% Senior Notes (due 2019) [Member]
Fair values and related carrying values of our debt instruments
Senior notes	499,382,000	499,351,000
Interest rate of senior notes	5.875%
5.875% Senior Notes (due 2019) [Member] \| Carrying Value [Member]
Fair values and related carrying values of our debt instruments
Senior notes	499,400,000	499,400,000
5.875% Senior Notes (due 2019) [Member] \| Fair Value [Member]
Fair values and related carrying values of our debt instruments
Debt Instrument, Fair Value	558,200,000	550,900,000
5.70% Senior Notes (due 2039) [Member]
Fair values and related carrying values of our debt instruments
Senior notes	496,796,000	496,773,000
Interest rate of senior notes	5.70%
5.70% Senior Notes (due 2039) [Member] \| Carrying Value [Member]
Fair values and related carrying values of our debt instruments
Senior notes	496,800,000	496,800,000
5.70% Senior Notes (due 2039) [Member] \| Fair Value [Member]
Fair values and related carrying values of our debt instruments
Debt Instrument, Fair Value	$ 492,600,000	$ 493,100,000

Fair values and related carrying values of our debt instruments Abstract.

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Namespace Prefix:	do
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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity 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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6947722&loc=d3e13433-108611

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=6947722&loc=d3e13476-108611

+ Details

Name:	us-gaap_DebtInstrumentFairValue
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Interest rate stated in the contractual debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 22
-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
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Data Type:	num:percentItemType
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Period Type:	instant

- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 16
-Article 9

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16(a))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

Name:	us-gaap_SeniorNotes
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant