General Information (Details 1) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011 Rigs	Dec. 31, 2010 Rigs	Dec. 31, 2009 Rigs
Summary of cold stacked rigs evaluated for impairment
Total number of cold stacked rigs	8	7	4
Aggregate net book value	$ 76.5	$ 78.0	$ 20.2
Mid-Water floaters [Member]
Summary of cold stacked rigs evaluated for impairment
Total number of cold stacked rigs	3	3	1
Jack-ups [Member]
Summary of cold stacked rigs evaluated for impairment
Total number of cold stacked rigs	5	4	3