Derivative Instruments (Details 2) (USD $)	Mar. 31, 2012	Dec. 31, 2011
Fair value derivative assets and liabilities classified in condensed balance sheets
Derivative Assets, Current	$ 283,000	$ 6,117,000
Derivative Liabilities, Current	44,740,000	20,365,000
Total Derivative Assets	600,000	13,100,000
Derivative Assets, Noncurrent	276,000	7,027,000
Derivative Liabilities, Noncurrent	19,338,000	15,505,000
Total Derivative Liabilities	64,000,000	35,900,000
Commodity contract
Fair value derivative assets and liabilities classified in condensed balance sheets
Derivative Assets, Current	283,000	6,117,000
Derivative Liabilities, Current	44,740,000	20,365,000
Derivative Assets, Noncurrent	276,000	7,027,000
Derivative Liabilities, Noncurrent	$ 19,338,000	$ 15,505,000