Annual report pursuant to Section 13 and 15(d)

Business and Summary of Significant Accounting Principles (Asset Retirement Obligation) (Details)

v2.4.1.9
Business and Summary of Significant Accounting Principles (Asset Retirement Obligation) (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]      
Balance, beginning $ 26,802us-gaap_AssetRetirementObligation $ 16,280us-gaap_AssetRetirementObligation  
Liability incurred 4,268us-gaap_AssetRetirementObligationLiabilitiesIncurred 5,292us-gaap_AssetRetirementObligationLiabilitiesIncurred 660us-gaap_AssetRetirementObligationLiabilitiesIncurred
Additions upon the close of AWN   5,218gncma_AssetRetirementObligationAdditions  
Accretion expense 1,249us-gaap_AssetRetirementObligationAccretionExpense 77us-gaap_AssetRetirementObligationAccretionExpense 508us-gaap_AssetRetirementObligationAccretionExpense
Revision in estimate (355)us-gaap_AssetRetirementObligationRevisionOfEstimate    
Liability settled (24)us-gaap_AssetRetirementObligationLiabilitiesSettled (65)us-gaap_AssetRetirementObligationLiabilitiesSettled  
Balance, ending $ 31,940us-gaap_AssetRetirementObligation $ 26,802us-gaap_AssetRetirementObligation $ 16,280us-gaap_AssetRetirementObligation