Impairment of Natural Gas and Crude Oil Properties (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Continuing Operations:
Impairment of proved properties	$ 0	$ 0	$ 45,000	$ 0
Impairment of significantly unproved properties	671	154	825	308
Amortization of Individually Insignificant Unproved Properties	831	202	2,136	636
Total continuing operations	1,502	356	47,961	944
Discontinued operations:
Impairment of proved properties	0	14	3	79
Total discontinued operations	0	14	3	79
Total impairment of crude oil and natural gas properties	$ 1,502	$ 370	$ 47,964	$ 1,023