Derivative Financial Instruments (Details 3) (USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Derivative instruments, Balance Sheet Location
Derivatives assets - current	$ 1,254,000	$ 1,061,000
Derivatives assets-long-term	2,135,000
Derivatives liabilities - current	(7,000,000)	(20,377,000)
Derivatives liabilities - long-term	(1,202,000)	(3,226,000)
Total	(4,813,000)	(22,542,000)
Commodity derivatives | Not designated as hedging instruments
Derivative instruments, Balance Sheet Location
Derivatives assets - current	1,254,000	1,061,000
Derivatives assets-long-term	2,135,000
Derivatives liabilities - current	(4,330,000)	(17,005,000)
Derivatives liabilities - long-term		(659,000)
Cash settlements made on commodity derivative contracts which were settled in the month subsequent to period end	600,000	3,400,000
Deferred premiums related to commodity derivative contracts	5,000,000	7,600,000
Deferred premiums related to commodity derivative contracts	1,100,000	2,400,000
Oil derivative contracts
Derivative instruments, Balance Sheet Location
Derivatives assets - current	1,300,000
Provisional Oil Sales
Derivative instruments, Balance Sheet Location
Derivatives assets - current		1,100,000
Interest rate contracts | Not designated as hedging instruments
Derivative instruments, Balance Sheet Location
Derivatives liabilities - current	(2,670,000)	(3,372,000)
Derivatives liabilities - long-term	$ (1,202,000)	$ (2,567,000)