Quarterly report pursuant to Section 13 or 15(d)

Subsequent Event (Details)

v2.4.1.9
Subsequent Event (Details) (Senior Notes, USD $)
 0 Months Ended 3 Months Ended
Apr. 01, 2015
Jun. 30, 2015
6.875% Senior Notes due 2025 | Subsequent Event
    
Subsequent Event [Line Items]    
Debt face amount $ 450,000,000.0us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= gncma_SeniorNotes6.875Percentdue2025Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember 		 
Debt stated percentage 6.875%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= gncma_SeniorNotes6.875Percentdue2025Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember 		 
Debt issuance price, percent 99.105%gncma_DebtInstrumentIssuancePricePercent
/ us-gaap_DebtInstrumentAxis
= gncma_SeniorNotes6.875Percentdue2025Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember 		 
Closing costs 7,700,000us-gaap_DebtIssuanceCosts
/ us-gaap_DebtInstrumentAxis
= gncma_SeniorNotes6.875Percentdue2025Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember 		 
Scenario, Forecast | Senior Notes Due 2019    
Subsequent Event [Line Items]    
Loss on extinguishment of debt   $ 27,700,000us-gaap_GainsLossesOnExtinguishmentOfDebt
/ us-gaap_DebtInstrumentAxis
= gncma_SeniorNotesDueTwentyNineteenMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember