Share Based Compensation (Summary Of Non-Vested Share Award Related Compensation Expense Recognized) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Non-vested share award related compensation expense	$ 10.6	$ 11.7	$ 6.7
Tax benefit	(1.1)	(1.6)	(0.9)
Total non-vested share award related compensation expense included in net income	16.4	14.2	9.8
Contract drilling
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Non-vested share award related compensation expense	8.8	6.8	3.9
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Non-vested share award related compensation expense	8.7	9.0	6.8
Operating Expenses [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Non-vested share award related compensation expense	$ 17.5	$ 15.8	$ 10.7

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479830/718-10-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

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