Supplementary Financial Information for Oil and Gas Producing Activities (Unaudited) (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($) MMcf MMBbls	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($) MMcf MMBbls	Dec. 31, 2014 USD ($) MMcf MMBbls	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($) MMcf MMBbls	Dec. 31, 2015 USD ($) a $ / MMcf $ / MBbls MMcf MMBbls	Dec. 31, 2014 USD ($) $ / MMcf $ / MBbls MMcf MMBbls	Dec. 31, 2013 USD ($) $ / MMcf $ / MBbls MMcf MMBbls	Dec. 31, 2015 USD ($) MMcf MMBbls	Dec. 31, 2014 USD ($) MMcf MMBbls	Dec. 31, 2013 USD ($) MMcf MMBbls
Supplementary Financial Information for Oil and Gas Producing Activities (Unaudited)
Area of land (in acres) | a									3,800
Area of land under a lease (in acres) | a									538
Results of Operations
Revenues	$ 497	$ 577	$ 671	$ 702	$ 1,060	$ 1,218	$ 1,356	$ 1,640	$ 2,447	$ 5,274	$ 5,762
Production and operating costs									1,259	1,546	1,920
Depreciation and depletion									874	895	955
Results of operations before income taxes									314	2,833	2,887
Income tax expense									(19)	742	736
Results of operations (excluding corporate overhead and interest costs)									333	2,091	2,151
Costs Incurred
Development costs incurred									14	25	58
Capitalized Costs
Natural gas properties - proved												$ 18,398	$ 18,384	$ 18,359
Less: accumulated depreciation and depletion												10,030	9,153	8,256
Net capitalized costs for natural gas properties												8,368	9,231	10,103
Unaudited standardized measure of discounted future net cash flows
Future estimated gross revenues												25,916	60,073	61,873
Future estimated production and development costs									(12,019)	(23,243)	(24,276)
Future estimated net revenues									13,897	36,830	37,597
Future estimated income tax expense												(3,642)	(10,105)	(10,286)
Future estimated net cash flows												10,255	26,725	27,311
10% annual discount for estimated timing of cash flows												(4,969)	(13,437)	(13,733)
Standardized measure of discounted future estimated net cash flows	5,286			13,288	13,288			13,578	13,288	13,578	12,764	$ 5,286	$ 13,288	$ 13,578
Changes in standardized measure of discounted future net cash flows
Standardized measure - beginning of year				$ 13,288				$ 13,578	13,288	13,578	12,764
Net change in sales prices and production costs									(12,535)	2,180	4,227
Sales of natural gas produced, net of production costs									(1,188)	(3,730)	(3,842)
Net change due to changes in quantity estimates									(2,625)	(586)	430
Previously estimated development costs incurred									14	21	56
Net change in income taxes									3,147	90	(380)
Accretion of discount									1,570	1,594	1,486
Timing of production of reserves and other									3,615	141	(1,163)
Standardized measure - end of year	$ 5,286				$ 13,288				$ 5,286	$ 13,288	$ 13,578
Natural Gas (BCF)
Reserve Quantities
Price (in dollars per Mcf or Bbl) | $ / MMcf									2.80	4.61	3.88
Changes in proved reserves
Proved reserves - beginning of year | MMcf				6,700				7,600	6,700	7,600	8,300
Revisions of previous estimates | MMcf									(900)	(300)
Production | MMcf									(500)	(600)	(700)
Proved reserves - end of year | MMcf	5,300				6,700				5,300	6,700	7,600
Proved developed reserves - end of year | MMcf												5,300	6,700	7,600
Natural Gas Liquids (MMBLS)
Reserve Quantities
Price (in dollars per Mcf or Bbl) | $ / MBbls									14.92	30.20	29.95
Changes in proved reserves
Proved reserves - beginning of year | MMBbls				1.0				1.1	1.0	1.1	1.1
Revisions of previous estimates | MMBbls									(0.2)		0.1
Production | MMBbls									(0.1)	(0.1)	(0.1)
Proved reserves - end of year | MMBbls	0.7				1.0				0.7	1.0	1.1
Proved developed reserves - end of year | MMBbls												0.7	1.0	1.1