Drilling And Other Property And Equipment (Narrative) (Detail) (USD $)	Sep. 30, 2012 Vessel	Dec. 31, 2011
Property, Plant and Equipment [Line Items]
Construction work-in-progress	$ 870,192,000	$ 504,805,000
Number of drillships under construction
Four Drillships [Member]
Property, Plant and Equipment [Line Items]
Construction work-in-progress	699,100,000
Ocean Onyx [Member]
Property, Plant and Equipment [Line Items]
Construction work-in-progress	141,700,000
Ocean Apex [Member]
Property, Plant and Equipment [Line Items]
Construction work-in-progress	29,400,000
Jack-Up Rigs [Member]
Property, Plant and Equipment [Line Items]
Pre-tax gain on sale of rigs	76,500,000
Net book value of assets retired	$ 55,400,000
Number of rigs sold during period	6