Beluga River Unit (Narrative) (Details)		3 Months Ended		6 Months Ended
	Feb. 04, 2016 USD ($) a	Jun. 30, 2016 USD ($) MMcf	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) mi MMcf	Jun. 30, 2015 USD ($)	Apr. 22, 2016 MMcf
Business Acquisition [Line Items]
Revenue		$ 44,622,517	$ 47,697,820	$ 94,872,652	$ 122,670,937
Beluga River Unit [Member]
Business Acquisition [Line Items]
Date of Purchase and Sale Agreement				Feb. 04, 2016
Total purchase price	$ 152,000,000
Cash consideration		$ 44,183,293		$ 44,183,293
Working interest ownership percentage	30.00%	10.00%		10.00%
Number of lease acres | a	15,500
Number of lease acres in Unit / Participating Area | a	8,200
Number of lease acres held by Unit | a	7,300
Closing date of Purchase and Sale Agreement				Apr. 22, 2016
Number of miles from Anchorage | mi				35
Acquisition costs		$ 1,400,000		$ 1,400,000
Amount of gas acquired | MMcf		68,354		68,354		69,099
Expiration date of gas sales				Dec. 31, 2017
Revenue				$ 800,000
Lifted amount of gas in proven developed reserves | MMcf		900		900
Remaining amount of gas in proven developed reserves | MMcf		26,100		26,100
Municipal Light & Power [Member] | Beluga River Unit [Member]
Business Acquisition [Line Items]
Working interest ownership percentage	70.00%	56.70%		56.70%		33.30%
ConocoPhillips (COP) [Member] | Beluga River Unit [Member]
Business Acquisition [Line Items]
Working interest ownership percentage						33.30%
ConocoPhillips (COP) [Member] | Deep Oil Resources [Member]
Business Acquisition [Line Items]
Working interest ownership percentage	67.00%
Hilcorp Alaska, LLC [Member] | Beluga River Unit [Member]
Business Acquisition [Line Items]
Working interest ownership percentage		33.30%		33.30%		33.30%
Minimum [Member] | Beluga River Unit [Member]
Business Acquisition [Line Items]
Effective annual cost savings				$ (2,000,000)
Maximum [Member] | Beluga River Unit [Member]
Business Acquisition [Line Items]
Effective annual cost savings				$ (3,000,000)
ENSTAR [Member] | ConocoPhillips (COP) [Member]
Business Acquisition [Line Items]
Expiration year of Gas Sale and Purchase Agreement				2017