Annual report pursuant to Section 13 and 15(d)

Asset Impairment - Additional Information (Detail)

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Asset Impairment - Additional Information (Detail) (USD $)
3 Months Ended 12 Months Ended
Dec. 31, 2011
Rigs
Dec. 31, 2011
Rigs
Impaired Long-Lived Assets Held and Used [Line Items]    
Number of rigs combined 2 2
Current estimated cost of rigs $ 385,000,000 $ 385,000,000
Estimated total capitalized interest 50,700,000 50,700,000
Carrying value of rigs 339,500,000 339,500,000
Impairments and other charges 170,000,000 170,000,000
Asset Impairment charge after tax 109,100,000  
Fair value of rigs $ 169,500,000 $ 169,500,000
Discounted rate of interests 10.00%