Supplementary Financial Information for Oil and Gas Producing Activities (Unaudited) (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($) MMcf MMBbls	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($) MMcf MMBbls	Dec. 31, 2015 USD ($) MMcf MMBbls	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($) MMcf MMBbls	Dec. 31, 2016 USD ($) a $ / MMcf $ / MBbls MMcf MMBbls	Dec. 31, 2015 USD ($) $ / MMcf $ / MBbls MMcf MMBbls	Dec. 31, 2014 USD ($) $ / MMcf $ / MBbls MMcf MMBbls	Dec. 31, 2016 USD ($) MMcf MMBbls	Dec. 31, 2015 USD ($) MMcf MMBbls	Dec. 31, 2014 USD ($) MMcf MMBbls
Reserve Quantities
Area of land (in acres) | a									3,800
Area of land under a lease (in acres) | a									538
Unaudited standardized measure of discounted future net cash flows
Future estimated gross revenues												$ 17,908	$ 25,916	$ 60,073
Future estimated production and development costs									$ (8,402)	$ (12,019)	$ (23,242)
Future estimated net revenues									9,506	13,897	36,831
Future estimated income tax expense												(2,458)	(3,642)	(10,105)
Future estimated net cash flows												7,048	10,255	26,726
10% annual discount for estimated timing of cash flows												(2,851)	(4,969)	(13,438)
Standardized measure of discounted future estimated net cash flows	$ 4,197			$ 5,286	$ 5,286			$ 13,288	5,286	13,288	13,578	4,197	5,286	13,288
Changes in standardized measure of discounted future net cash flows
Standardized measure - beginning of year				5,286				13,288	5,286	13,288	13,578
Net change in sales prices and production costs									(1,403)	(12,535)	2,180
Sales of natural gas produced, net of production costs									(928)	(1,188)	(3,730)
Net change due to changes in quantity estimates									(1,732)	(2,625)	(586)
Previously estimated development costs incurred										14	21
Net change in income taxes									414	3,147	90
Accretion of discount									571	1,570	1,594
Timing of production of reserves and other									1,989	3,615	141
Standardized measure - end of year	4,197				5,286				4,197	5,286	13,288
Results of Operations
Revenues	$ 602	$ 554	$ 504	$ 432	$ 497	$ 577	$ 671	$ 702	2,092	2,447	5,274
Production and operating costs									1,164	1,259	1,546
Depreciation and depletion									868	874	895
Results of operations before income taxes									60	314	2,833
Income tax (benefit) expense									(93)	(19)	742
Results of operations (excluding corporate overhead and interest costs)									153	333	2,091
Costs Incurred
Development costs incurred									$ 15	$ 15	$ 25
Capitalized Costs
Natural gas properties - proved												18,412	18,398	18,384
Less: accumulated depreciation and depletion												10,900	10,030	9,153
Net capitalized costs for natural gas properties												$ 7,512	$ 8,368	$ 9,231
Natural Gas (BCF)
Reserve Quantities
Price (in dollars per Mcf or Bbl) | $ / MMcf									2.65	2.80	4.61
Changes in proved reserves
Proved reserves - beginning of year | MMcf				5,300				6,700	5,300	6,700	7,600
Revisions of previous estimates | MMcf									(900)	(900)	(300)
Production | MMcf									(500)	(500)	(600)
Proved reserves - end of year | MMcf	3,900				5,300				3,900	5,300	6,700
Proved developed reserves - end of year | MMcf												3,900	5,300	6,700
Natural Gas Liquids (MMBLS)
Reserve Quantities
Price (in dollars per Mcf or Bbl) | $ / MBbls									16.61	14.92	30.20
Changes in proved reserves
Proved reserves - beginning of year | MMBbls				0.7				1.0	0.7	1.0	1.1
Revisions of previous estimates | MMBbls									(0.1)	(0.2)
Production | MMBbls									(0.1)	(0.1)	(0.1)
Proved reserves - end of year | MMBbls	0.5				0.7				0.5	0.7	1.0
Proved developed reserves - end of year | MMBbls												0.5	0.7	1.0