Summary of Significant Accounting Policies (Details) (USD $)	12 Months Ended			1 Months Ended								5 Months Ended	7 Months Ended										12 Months Ended		12 Months Ended																12 Months Ended
	Dec. 31, 2012 mi	Dec. 31, 2011	Dec. 31, 2010	Mar. 31, 2013 Commodity Contract [Member] MMBTU	Feb. 28, 2013 Commodity Contract [Member] MMBTU	Jan. 31, 2013 Commodity Contract [Member] MMBTU bbl Contract	May 31, 2012 Commodity Contract [Member] bbl	Apr. 30, 2012 Commodity Contract [Member] bbl	Mar. 31, 2012 Commodity Contract [Member] bbl	Feb. 29, 2012 Commodity Contract [Member] bbl	Jan. 31, 2012 Commodity Contract [Member] bbl Contract	Jun. 30, 2013 Commodity Contract [Member] bbl	Dec. 31, 2012 Commodity Contract [Member] bbl Contract	Dec. 31, 2011 Commodity Contract [Member] Contract	Dec. 31, 2012 Commodity Contract [Member] Not Designated as Hedging Instrument [Member] Current Assets [Member]	Dec. 31, 2011 Commodity Contract [Member] Not Designated as Hedging Instrument [Member] Current Assets [Member]	Dec. 31, 2012 Commodity Contract [Member] Not Designated as Hedging Instrument [Member] Other Assets [Member]	Dec. 31, 2011 Commodity Contract [Member] Not Designated as Hedging Instrument [Member] Other Assets [Member]	Dec. 31, 2012 Commodity Contract [Member] Not Designated as Hedging Instrument [Member] Current Liabilities [Member]	Dec. 31, 2011 Commodity Contract [Member] Not Designated as Hedging Instrument [Member] Current Liabilities [Member]	Dec. 31, 2012 Commodity Contract [Member] Not Designated as Hedging Instrument [Member] Other Liabilities [Member]	Dec. 31, 2011 Commodity Contract [Member] Not Designated as Hedging Instrument [Member] Other Liabilities [Member]	Dec. 31, 2012 Wells Fargo Bank [Member]	Dec. 31, 2011 Wells Fargo Bank [Member]	Dec. 31, 2012 Minimum [Member]	Dec. 31, 2012 Maximum [Member]	Dec. 31, 2012 Producing Oil and Gas Properties [Member]	Dec. 31, 2011 Producing Oil and Gas Properties [Member]	Dec. 31, 2010 Producing Oil and Gas Properties [Member]	Dec. 31, 2012 Producing Oil and Gas Properties Impaired in 2012 [Member]	Dec. 31, 2011 Producing Oil and Gas Properties Impaired in 2011 [Member]	Dec. 31, 2012 Non-Producing Oil and Gas Properties [Member]	Dec. 31, 2011 Non-Producing Oil and Gas Properties [Member]	Dec. 31, 2010 Non-Producing Oil and Gas Properties [Member]	Dec. 31, 2012 South Texas Project acreage [Member]	Dec. 31, 2011 South Texas Project acreage [Member]	Dec. 31, 2012 West Texas Project [Member]	Dec. 31, 2011 West Texas Project [Member]	Dec. 31, 2012 Napoleonville, Louisiana acreage [Member]	Dec. 31, 2011 Napoleonville, Louisiana acreage [Member]	Dec. 31, 2012 Other acreage areas [Member]	Dec. 31, 2011 Other acreage areas [Member]
Nature of Operations [Abstract]
Primary area of operation (in miles)	1,000
Allowance for Doubtful Accounts [Abstract]
Percentage of crude oil and natural gas sales in accounts receivable (in hundredths)	90.00%
Number of days, cash is received from transaction date	25 days
Components of prepayments and other [Abstract]
Cash collateral deposits for commodity purchases	$ 5,000,000	$ 6,521,000
Insurance premiums	1,872,000	2,033,000
Commodity imbalances and futures	353,000	1,452,000
Rents, license and other	867,000	645,000
Prepayments, total	8,092,000	10,651,000
Property, Plant and Equipment [Line Items]
Exploratory drilling costs	0
Property and equipment, useful life																									3 years	20 years
Fair value measurements for producing oil and gas properties that were subject to fair value impairment [Abstract]
Net book value at January 1																														11,073,000	8,704,000										475,000
Property additions	23,335,000	24,890,000	11,761,000																											13,083,000	16,465,000										810,000
Depletion taken																														(6,371,000)	(6,633,000)
Property sale																																									(100,000)
Impairment valuation loss	(5,555,000)	(14,749,000)	(2,224,000)																								(4,699,000)	(7,105,000)	(946,000)	(4,699,000)	(7,105,000)	(856,000)	(7,644,000)	(1,277,000)							(856,000)
Net book at December 31																														13,086,000	11,431,000										329,000
Capitalized costs for non producing oil and gas leasehold interests specified as percentage of total costs (in hundredths)																																4.00%
Total Non-producing Leasehold Costs	4,095,000	3,295,000																																	3,263,000	2,212,000	180,000	288,000	323,000	320,000	329,000	475,000
Proceeds from sale of oil and gas properties																											3,049,000	6,200,000				578,000	329,000
Pre-tax gain on sale of oil and gas properties	2,203,000	2,923,000	0																								1,728,000	2,708,000				475,000	125,000
Pre-tax gain on sale of equipment	2,617,000	1,024,000
Cash Deposits and Other Assets [Abstract]
Insurance collateral deposits	3,413,000	3,331,000
State collateral deposits	170,000	168,000
Materials and supplies	616,000	668,000
Cash deposits and other	4,199,000	4,167,000
Revenue Recognition [Abstract]
Increase in the entity's reported revenue	1,381,352,000	1,812,561,000	1,415,844,000
Letter of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity																							60,000,000
Standby letters of credit issued																							21,900,000	38,900,000
Covenant terms																							Such restrictions included the maintenance of a combined 1.1 to 1.0 current ratio and the maintenance of positive net earnings excluding inventory valuation changes, as defined, among other restrictions. The Company is currently in compliance with all such financial covenants.
Current ratio																							1.1
Statement of Cash Flows [Abstract]
Interest paid	10,000	8,000	36,000
Income taxes paid	12,650,000	5,597,000	532,000
Proceeds from income tax refunds	10,000	2,743,000	0
Capital expenditures incurred but not yet paid	2,419,000	4,070,000	2,868,000
Earnings Per Share [Abstract]
Weighted average number of shares outstanding (in shares)	4,217,596	4,217,596	4,217,596
Contracts at gross valuation [Abstract]
Asset Derivatives															688,000	3,500,000	0	0	0	0	0	0
Liability Derivatives															0	0	0	0	682,000	2,117,000	0	0
Less Counterparty Offsets															(270,000)	(1,436,000)	0	0	(270,000)	(1,436,000)	0	0
As Reported Fair Value Contracts															$ 418,000	$ 2,064,000	$ 0	$ 0	$ 412,000	$ 681,000	$ 0	$ 0
Number of purchase and sales contracts held													24	13
Volume of crude oil purchased and sold per day under derivative contracts (in barrels)						900	1,800	5,700	5,800	6,100	2,800	200	1,800
Volume of natural gas purchased and sold per day under derivative contracts (in mmbtu)				41,000	1,000	172,000