SUPPLEMENTAL FINANCIAL DATA-OIL AND GAS PRODUCING ACTIVITIES (Results of Operations for Oil and Gas Producing Activities) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Results of Operations for Oil and Gas Producing Activities
Oil, natural gas, and natural gas liquids sales	$ 441,341	$ 605,523	$ 703,531
Expenses:
Production expense	103,427	156,909	153,518
Depletion expense	165,767	275,886	213,866
Ceiling test write-down of oil and natural gas properties	57,636	992,404
Accretion of asset retirement obligations	2,834	6,549	6,017
Income tax benefit	(707)	173,437	89,135
Total expenses	328,957	1,605,185	462,536
Results of operations from oil and gas producing activities	112,384	(999,662)	240,995
Depletion rate per Mcfe (in dollars per Mcfe)	2.20	2.28	1.75
United States
Results of Operations for Oil and Gas Producing Activities
Oil, natural gas, and natural gas liquids sales	441,341	605,523	703,531
Expenses:
Production expense	103,427	156,909	153,518
Depletion expense	165,767	275,886	213,866
Ceiling test write-down of oil and natural gas properties	57,636	957,587
Accretion of asset retirement obligations	2,760	6,487	5,973
Income tax benefit	(707)	173,437	89,135
Total expenses	328,883	1,570,306	462,492
Results of operations from oil and gas producing activities	112,458	(964,783)	241,039
Depletion rate per Mcfe (in dollars per Mcfe)	2.20	2.28	1.75
Italy
Results of Operations for Oil and Gas Producing Activities
Oil, natural gas, and natural gas liquids sales	0	0	0
Expenses:
Production expense	0	0	0
Depletion expense	0	0	0
Ceiling test write-down of oil and natural gas properties	0	34,817
Accretion of asset retirement obligations	74	62	44
Income tax benefit	0	0	0
Total expenses	74	34,879	44
Results of operations from oil and gas producing activities	$ (74)	$ (34,879)	$ (44)
Depletion rate per Mcfe (in dollars per Mcfe)	0	0	0