Quarterly report pursuant to Section 13 or 15(d)

Business and Summary of Significant Accounting Principles (Business Acquisition) (Details)

v2.4.1.9
Business and Summary of Significant Accounting Principles (Business Acquisition) (Details) (USD $)
 0 Months Ended 3 Months Ended
Feb. 02, 2015
Mar. 31, 2015
Property, Plant and Equipment [Line Items]    
Total consideration transfered to ACS $ 304,838,000gncma_ConsiderationTransferredtoAcquireAssetsandInterest  
AWN non-controlling interest 303,831,000us-gaap_MinorityInterestDecreaseFromRedemptions 303,831,000us-gaap_MinorityInterestDecreaseFromRedemptions
Property and equipment 746,000us-gaap_PropertyPlantAndEquipmentAdditions  
Other intangible assets 261,000us-gaap_PaymentsToAcquireIntangibleAssets  
Noncontrolling Interest [Member]    
Property, Plant and Equipment [Line Items]    
AWN non-controlling interest 268,364,000us-gaap_MinorityInterestDecreaseFromRedemptions
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember 		268,364,000us-gaap_MinorityInterestDecreaseFromRedemptions
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember
Additional Paid-in Capital [Member]    
Property, Plant and Equipment [Line Items]    
AWN non-controlling interest 35,467,000us-gaap_MinorityInterestDecreaseFromRedemptions
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AdditionalPaidInCapitalMember 		35,467,000us-gaap_MinorityInterestDecreaseFromRedemptions
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AdditionalPaidInCapitalMember
Rights to Receive Future Capacity [Member]    
Property, Plant and Equipment [Line Items]    
Fair value adjustment to assets 1,200,000us-gaap_AssetsFairValueAdjustment
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= gncma_RightstoReceiveFutureCapacityMember 		 
Rights to Use Capacity [Member]    
Property, Plant and Equipment [Line Items]    
Impairment of intangible assets 3,800,000us-gaap_ImpairmentOfIntangibleAssetsFinitelived
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= gncma_RightstoUseCapacityMember 		 
ACS Wireless [Member]    
Property, Plant and Equipment [Line Items]    
Consideration paid $ 293,200,000gncma_PaymentstoAcquireAssetsandInterest
/ us-gaap_BusinessAcquisitionAxis
= gncma_ACSWirelessMember