Principal Charges Account (Schedule Of Principal Charges) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Principal Charges Account [Abstract]
Attorneys' fees and expenses	$ 1,024,834gni_LegalFeesCumulative	$ 1,024,834gni_LegalFeesCumulative
Costs of surface lands	6,606,815us-gaap_AcquisitionCostsCumulative	6,606,815us-gaap_AcquisitionCostsCumulative
Cumulative shipment credits	(2,549,174)gni_ShipmentCreditsCumulative	(2,471,015)gni_ShipmentCreditsCumulative
Cumulative asset disposition credits	(372,124)gni_AssetDispositionCreditsCumulative	(372,124)gni_AssetDispositionCreditsCumulative
Principal Charges account balance	$ 4,710,351gni_PrincipalChargesAccountBalance	$ 4,788,510gni_PrincipalChargesAccountBalance

The capitalized costs incurred (excluded from amortization), as of the date of the balance sheet, to purchase, lease or otherwise acquire an unproved property, including costs of lease bonuses and options to purchase or lease properties, the portion of costs applicable to minerals when land including mineral rights is purchased in fee, brokers' fees, recording fees, legal costs, and other costs incurred in acquiring properties.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-10.(c)(7)(ii))

-URI http://asc.fasb.org/extlink&oid=27015464&loc=d3e511914-122862

Name:	us-gaap_AcquisitionCostsCumulative
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant