Annual report pursuant to Section 13 and 15(d)

Long Term Debt (Schedule of Long Term Debt Applicable Margin) (Details)

v2.4.1.9
Long Term Debt (Schedule of Long Term Debt Applicable Margin) (Details) (London Interbank Offered Rate (LIBOR))
 12 Months Ended
Dec. 31, 2014
Greater than or equal to 5.5
  
Debt Instrument [Line Items]  
Basis spread on variable rate 3.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ gncma_InterestRateLeverageRatioAxis
= gncma_LeverageRatioRangeOneMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember
Greater than or equal to 5.0 but less than or equal to 5.5
  
Debt Instrument [Line Items]  
Basis spread on variable rate 2.75%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ gncma_InterestRateLeverageRatioAxis
= gncma_LeverageRatioRangeTwoMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember
Greater than or equal to 4.5 but less than or equal to 5.0
  
Debt Instrument [Line Items]  
Basis spread on variable rate 2.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ gncma_InterestRateLeverageRatioAxis
= gncma_LeverageRatioRangeThreeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember
Greater than or equal to 4.0 but less than or equal to 4.5
  
Debt Instrument [Line Items]  
Basis spread on variable rate 2.25%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ gncma_InterestRateLeverageRatioAxis
= gncma_LeverageRatioRangeFourMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember
Less than 4.0
  
Debt Instrument [Line Items]  
Basis spread on variable rate 2.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ gncma_InterestRateLeverageRatioAxis
= gncma_LeverageRatioRangeFiveMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember