The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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General description of claims, deemed to be reimbursable and included in accounts receivable, relating to the termination of long-term government contracts and programs. Includes claims associated with terminated war and defense contracts. If a reasonable estimate of a termination claim is undeterminable or impossible to make, disclosure is made to discuss the status and circumstances related to the undeterminable claim.

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Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified		12 Months Ended
	Mar. 31, 2013	Dec. 31, 2010 Legal Reserve	Dec. 31, 2012 Contract Drilling	Dec. 31, 2012 Maximum Contract Drilling
Commitments and Contingencies Disclosure [Line Items]
Contract term				3 years
Contract termination claims description			early termination provisions that would require us to pay penalties if we terminate the agreements prior to the end of their original terms.
Loss on contract termination for default			$ 3.8
Reserve established for contingency matters		0.9
Suspense account	1.8
Asset retirement obligations	$ 4.6