Property and Equipment Changes in Capitalized Exploratory Drilling Costs (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 Well	Dec. 31, 2011 Well	Dec. 31, 2010 Well
Number of Wells
Balance at beginning of year (in wells)	0	1	0
Additions pending determination of proved reserves (in wells)	1	0	1
Reclassification to wells, equipment and facilities based on the determination of proved reserves (in wells)	0	0	0
Charged to exploration expense (in wells)	0	(1)	0
Balance at end of year (in wells)	1	0	1
Cost
Balance at beginning of year	$ 0	$ 6,180	$ 0
Additions pending determination of proved reserves	4,435	0	6,180
Reclassification to wells, equipment and facilities based on the determination of proved reserves	0	0	0
Charged to exploration expense	0	(6,180)	0
Balance at end of year	$ 4,435	$ 0	$ 6,180