Supplementary Financial Information for Oil and Gas Producing Activities (Unaudited) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014 acre	Dec. 31, 2013	Dec. 31, 2012
Supplementary Financial Information for Oil and Gas Producing Activities (Unaudited)
Area of land (in acres)									3,800
Area of land under a lease (in acres)									538
Results of Operations
Revenues	$ 1,060	$ 1,218	$ 1,356	$ 1,640	$ 1,443	$ 1,401	$ 1,488	$ 1,430	$ 5,274	$ 5,762	$ 7,121
Production and operating costs									1,546	1,920	1,891
Depreciation and depletion									895	955	1,291
Results of operations before income taxes									2,833	2,887	3,939
Income tax expense									742	736	1,044
Results of operations (excluding corporate overhead and interest costs)									2,091	2,151	2,895
Costs Incurred
Development costs incurred									25	58	81
Capitalized Costs
Natural gas properties - proved	18,384				18,359				18,384	18,359	18,301
Less: accumulated depreciation and depletion	9,153				8,256				9,153	8,256	7,294
Net capitalized costs for natural gas properties	9,231				10,103				9,231	10,103	11,007
Unaudited standardized measure of discounted future net cash flows
Future estimated gross revenues	60,073				61,873				60,073	61,873	57,882
Future estimated production and development costs									(23,243)	(24,276)	(23,905)
Future estimated net revenues									36,830	37,597	33,977
Future estimated income tax expense	(10,105)				(10,286)				(10,105)	(10,286)	(9,193)
Future estimated net cash flows	26,725				27,311				26,725	27,311	24,784
10% annual discount for estimated timing of cash flows	(13,437)				(13,733)				(13,437)	(13,733)	(12,020)
Standardized measure of discounted future estimated net cash flows	13,288				13,578				13,288	13,578	12,764
Changes in standardized measure of discounted future net cash flows
Standardized measure - beginning of year				13,578				12,764	13,578	12,764	29,948
Net change in sales prices and production costs									2,180	4,227	(7,067)
Sales of natural gas produced, net of production costs									(3,730)	(3,842)	(5,230)
Net change due to changes in quantity estimates									(586)	430	(5,863)
Previously estimated development costs incurred									21	56	116
Net change in income taxes									90	(380)	7,419
Accretion of discount									1,594	1,486	1,603
Timing of production of reserves and other									141	(1,163)	(8,162)
Standardized measure - end of year	$ 13,288				$ 13,578				$ 13,288	$ 13,578	$ 12,764
Natural Gas (BCF)
Reserve Quantities
Price (in dollars per Mcf or Bbl)									4.61	3.88	2.87
Changes in proved reserves
Proved reserves - beginning of year				7,600.0				8,300.0	7,600.0	8,300.0	10,300.0
Revisions of previous estimates									(300.0)		(800.0)
Production									(600.0)	(700.0)	(1,200.0)
Proved reserves - end of year	6,700.0				7,600.0				6,700.0	7,600.0	8,300.0
Proved developed reserves - end of year	6,700.0				7,600.0				6,700.0	7,600.0	8,300.0
Natural Gas Liquids (MMBLS)
Reserve Quantities
Price (in dollars per Mcf or Bbl)									30.20	29.95	30.27
Changes in proved reserves
Proved reserves - beginning of year				1.1				1.1	1.1	1.1	1.5
Revisions of previous estimates										0.1	(0.3)
Production									(0.1)	(0.1)	(0.1)
Proved reserves - end of year	1.0				1.1				1.0	1.1	1.1
Proved developed reserves - end of year	1.0				1.1				1.0	1.1	1.1