Impairment of Natural Gas and Crude Oil Properties (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended		3 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Divestitures and Assets Held for Sale	Mar. 31, 2013 Divestitures and Assets Held for Sale
Continuing Operations:
Impairment of proved properties	$ 3,750	$ 0	$ 48,750	$ 0	$ 3,800	$ 45,000
Impairment of significantly unproved properties	154	154	979	462
Amortization of Individually Insignificant Unproved Properties	568	234	2,704	870
Total continuing operations	4,472	388	52,433	1,332
Discontinued operations:
Impairment of proved properties	0	7	3	86
Total discontinued operations	0	7	3	86
Total impairment of crude oil and natural gas properties	$ 4,472	$ 395	$ 52,436	$ 1,418