Quarterly report pursuant to Section 13 or 15(d)

Consolidated Statements of Cash Flows Supplemental Disclosures (Non-cash investing and financing activities) (Details)

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Consolidated Statements of Cash Flows Supplemental Disclosures (Non-cash investing and financing activities) (Details) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Supplemental Cash Flow Elements [Abstract]    
Non-cash consideration for Wireless Acquisition $ 19,446gncma_TransferofIntangibleAssets $ 0gncma_TransferofIntangibleAssets
Non-cash additions for purchases of property and equipment 17,817us-gaap_CapitalExpendituresIncurredButNotYetPaid 9,779us-gaap_CapitalExpendituresIncurredButNotYetPaid
Asset retirement obligation additions to property and equipment 243us-gaap_AssetRetirementObligationLiabilitiesIncurred 361us-gaap_AssetRetirementObligationLiabilitiesIncurred
Net capital lease obligation 0us-gaap_CapitalLeaseObligationsIncurred 9,385us-gaap_CapitalLeaseObligationsIncurred
Distribution to non-controlling interest 0gncma_DistributiontoNoncontrollingInterest 4,167gncma_DistributiontoNoncontrollingInterest
Deferred compensation distribution denominated in shares $ 0us-gaap_OtherSignificantNoncashTransactionValueOfConsiderationGiven1 $ 617us-gaap_OtherSignificantNoncashTransactionValueOfConsiderationGiven1