Derivative Financial Instruments (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary of location and aggregate fair value of all derivative financial instruments recorded in the consolidated statements of operations
Realized gain on derivatives	$ 2,813	$ 3,371	$ 4,713	$ 3,063	$ 2,869	$ 1,435	$ 952	$ 1,850	$ 13,960	$ 7,106	$ 5,299
Unrealized gain (loss) on derivatives	(3,653)	(12,993)	15,114	(3,270)	3,604	2,870	332	(1,668)	(4,802)	5,138	3,139
Total									9,158	12,244	8,438
Revenues [Member]
Summary of location and aggregate fair value of all derivative financial instruments recorded in the consolidated statements of operations
Realized gain on derivatives									13,960	7,106	5,299
Unrealized gain (loss) on derivatives									(4,802)	5,138	3,139
Oil [Member] | Revenues [Member]
Summary of location and aggregate fair value of all derivative financial instruments recorded in the consolidated statements of operations
Realized gain on derivatives									2,047
Unrealized gain (loss) on derivatives									3,673	(544)
Natural Gas [Member] | Revenues [Member]
Summary of location and aggregate fair value of all derivative financial instruments recorded in the consolidated statements of operations
Realized gain on derivatives									11,892	7,106	5,299
Unrealized gain (loss) on derivatives									(8,700)	5,692	3,139
NGL's [Member] | Revenues [Member]
Summary of location and aggregate fair value of all derivative financial instruments recorded in the consolidated statements of operations
Realized gain on derivatives									21
Unrealized gain (loss) on derivatives									$ 225