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Oil and Gas Properties (Components of Exploration Expenses) (Details) (USD $)
In Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2011
Jun. 30, 2010
Jun. 30, 2011
Jun. 30, 2010
Oil and Gas Properties        
Delay rental and geological and geophysical costs $ 1,299 $ 1,182 $ 1,654 $ 1,528
Impairment of unproved properties 6,640 [1] 0 [1] 6,640 [1] 0 [1]
Dry hole expense 0 (10) (9) (190)
Total exploration expense $ 7,939 $ 1,172 $ 8,285 $ 1,338
[1] Reflects costs associated with a deepwater lease in which the term expired during the second quarter of 2011.