OIL AND GAS RESERVE DATA (UNAUDITED) (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves
Future cash inflows	$ 1,836,212,000	$ 1,708,079,000	$ 1,033,221,000
Future production costs and taxes	(574,959,000)	(514,968,000)	(466,507,000)
Future development costs	(303,062,000)	(254,982,000)	(84,606,000)
Future income tax expenses	(105,078,000)	(108,977,000)
Net future cash flows	853,113,000	829,152,000	482,108,000
Discounted at 10% for estimated timing of cash flows	(393,233,000)	(343,146,000)	(194,480,000)
Standardized measure of discounted future net cash flows	459,880,000	486,006,000	287,628,000
Changes in Standardized Measure of Discounted Future Net Cash Flows Related to Proved Oil and Gas Reserves
Sales, net of production costs and taxes	(88,725,000)	(72,734,000)	(59,430,000)
Discoveries and extensions	108,438,000	152,973,000	15,994,000
Purchases of reserves in place	4,966,000		721,000
Changes in prices and production costs	(17,286,000)	196,010,000	119,779,000
Revisions of quantity estimates	(39,172,000)	56,710,000	17,619,000
Development costs incurred	36,539,000	30,892,000	5,544,000
Net changes in development costs	(90,392,000)	(149,662,000)	(68,497,000)
Interest factor-accretion of discount	48,601,000	28,763,000	24,129,000
Net change in income taxes	5,037,000	(40,070,000)
Changes in production rates (timing) and other	5,868,000	(4,504,000)	(9,523,000)
Net (decrease) increase	(26,126,000)	198,378,000	46,336,000
Balance at beginning of year	486,006,000	287,628,000	241,292,000
Balance at end of year	459,880,000	486,006,000	287,628,000
Oil prices weighted by production over lives of proved reserves	104.27	104.75	73.30
Gas prices weighted by production over lives of proved reserves	2.51	3.21	4.13
Future cash flows estimated to be spent to develop proved undeveloped properties	$ 223,200,000