Share Based Compensation (Summary Of Non-Vested Share Award Related Compensation Expense Recognized) (Details) - USD ($) $ in Millions	4 Months Ended	8 Months Ended	12 Months Ended
Apr. 30, 2021	Dec. 31, 2021	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		$ 0.7	$ 11.7	$ 6.7
Tax benefit		(0.2)	(1.6)	(0.9)
Total non-vested share award related compensation expense included in net income		3.4	14.2	9.8
Contract Drilling [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Non-vested share award related compensation expense	$ 2.4	1.6	6.8	3.9
General And Administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Non-vested share award related compensation expense	2.4	2.0	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	$ 4.8	$ 3.6	$ 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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