Quarterly report pursuant to Section 13 or 15(d)

Long-Term Debt (Details)

v2.4.1.9
Long-Term Debt (Details) (USD $)
3 Months Ended 0 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Feb. 02, 2015
Debt Instrument [Line Items]      
Loan fees and other expenses $ 5,853,000us-gaap_PaymentsOfDebtIssuanceCosts $ 0us-gaap_PaymentsOfDebtIssuanceCosts  
Medium-term Notes [Member] | Amended Senior Credit Facility [Member]      
Debt Instrument [Line Items]      
Debt face amount     275,000,000.0us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= gncma_AmendedSeniorCreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MediumTermNotesMember
Percentage of principal payable     0.25%gncma_DebtInstrumentPeriodicPaymentPrincipalPercentage
/ us-gaap_DebtInstrumentAxis
= gncma_AmendedSeniorCreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MediumTermNotesMember
Loan fees and other expenses     5,900,000us-gaap_PaymentsOfDebtIssuanceCosts
/ us-gaap_DebtInstrumentAxis
= gncma_AmendedSeniorCreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MediumTermNotesMember
Medium-term Notes [Member] | Amended Senior Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member]      
Debt Instrument [Line Items]      
Spread on variable rate     3.75%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_DebtInstrumentAxis
= gncma_AmendedSeniorCreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MediumTermNotesMember
/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember
Interest rate floor     1.00%gncma_DebtInstrumentVariableRateFloor
/ us-gaap_DebtInstrumentAxis
= gncma_AmendedSeniorCreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MediumTermNotesMember
/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember
Unsecured Debt [Member] | Searchlight ALX, LP Promissory Note [Member]      
Debt Instrument [Line Items]      
Debt face amount     75,000,000.0us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= gncma_SearchlightALXLPPromissoryNoteMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember
Debt stated percentage     7.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= gncma_SearchlightALXLPPromissoryNoteMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember
Unamortized discount     $ 21,700,000.0us-gaap_DebtInstrumentUnamortizedDiscount
/ us-gaap_DebtInstrumentAxis
= gncma_SearchlightALXLPPromissoryNoteMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember
Common Stock - Class A [Member] | Stock Appreciation Rights (SARs) [Member]      
Debt Instrument [Line Items]      
Exercise price of stock appreciation rights (per share)     $ 13.00us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1
/ us-gaap_ClassOfWarrantOrRightAxis
= us-gaap_StockAppreciationRightsSARSMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
Stock Appreciation Rights     3,000,000us-gaap_ClassOfWarrantOrRightOutstanding
/ us-gaap_ClassOfWarrantOrRightAxis
= us-gaap_StockAppreciationRightsSARSMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
Stock Appreciation Rights issued for interest capitalization     4.00%gncma_PercentofRightPayableperDollarofCapitalizedInterest
/ us-gaap_ClassOfWarrantOrRightAxis
= us-gaap_StockAppreciationRightsSARSMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember