Annual report pursuant to Section 13 and 15(d)

Subsequent Events (Details)

v2.4.1.9
Subsequent Events (Details) (Subsequent Event [Member], USD $)
0 Months Ended
Feb. 02, 2015
ACS Wireless [Member]  
Subsequent Event [Line Items]  
Cash consideration paid $ 293,200,000us-gaap_PaymentsToAcquireBusinessesGross
/ us-gaap_BusinessAcquisitionAxis
= gncma_ACSWirelessMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
Medium-term Notes [Member] | Credit Agricole Fourth Amended and Restated Credit and Guarantee Agreement [Member]  
Subsequent Event [Line Items]  
Debt Instrument, face Amount 275,000,000.0us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= gncma_CreditAgricoleFourthAmendedandRestatedCreditandGuaranteeAgreementMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MediumTermNotesMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
Medium-term Notes [Member] | Credit Agricole Fourth Amended and Restated Credit and Guarantee Agreement [Member] | London Interbank Offered Rate (LIBOR)  
Subsequent Event [Line Items]  
Basis spread on variable rate 3.75%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_DebtInstrumentAxis
= gncma_CreditAgricoleFourthAmendedandRestatedCreditandGuaranteeAgreementMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MediumTermNotesMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember
Variable rate floor 1.00%gncma_DebtInstrumentVariableRateFloor
/ us-gaap_DebtInstrumentAxis
= gncma_CreditAgricoleFourthAmendedandRestatedCreditandGuaranteeAgreementMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MediumTermNotesMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember
Unsecured Debt [Member] | Searchlight ALX, LP Promissory Note [Member]  
Subsequent Event [Line Items]  
Debt Instrument, face Amount $ 75,000,000.0us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= gncma_SearchlightALXLPPromissoryNoteMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
Stated percentage 7.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= gncma_SearchlightALXLPPromissoryNoteMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
Class A Common Stock | Stock Appreciation Rights (SARs) [Member]  
Subsequent Event [Line Items]  
Rights outstanding 3,000,000us-gaap_ClassOfWarrantOrRightOutstanding
/ us-gaap_ClassOfWarrantOrRightAxis
= us-gaap_StockAppreciationRightsSARSMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
Exercise price of rights $ 13.00us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1
/ us-gaap_ClassOfWarrantOrRightAxis
= us-gaap_StockAppreciationRightsSARSMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember