Annual report pursuant to Section 13 and 15(d)

Income Taxes (Narratives) (Details)

v2.4.1.9
Income Taxes (Narratives) (Details) (USD $)
 3 Months Ended 12 Months Ended
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Operating Loss Carryforwards [Line Items]              
Income tax expense $ 1,400,000us-gaap_IncomeTaxExpenseBenefit $ 5,078,000us-gaap_IncomeTaxExpenseBenefit $ 2,355,000us-gaap_IncomeTaxExpenseBenefit $ 1,196,000us-gaap_IncomeTaxExpenseBenefit $ 10,029,000us-gaap_IncomeTaxExpenseBenefit $ 10,957,000us-gaap_IncomeTaxExpenseBenefit $ 12,088,000us-gaap_IncomeTaxExpenseBenefit
Federal statutory income tax rate         35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate    
Unrecognized tax benefits 0us-gaap_UnrecognizedTaxBenefits       0us-gaap_UnrecognizedTaxBenefits 0us-gaap_UnrecognizedTaxBenefits 0us-gaap_UnrecognizedTaxBenefits
Income tax interest expense         0us-gaap_IncomeTaxExaminationInterestExpense 0us-gaap_IncomeTaxExaminationInterestExpense 0us-gaap_IncomeTaxExaminationInterestExpense
Income tax penalties expense         0us-gaap_IncomeTaxExaminationPenaltiesExpense 0us-gaap_IncomeTaxExaminationPenaltiesExpense 0us-gaap_IncomeTaxExaminationPenaltiesExpense
Unrecognized tax benefits resulting in net operating loss carryforward 3,500,000us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic       3,500,000us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic    
Alternative Minimum Tax Credit Carryforward              
Operating Loss Carryforwards [Line Items]              
Tax credit carryforward, amount 1,700,000us-gaap_TaxCreditCarryforwardAmount
/ us-gaap_TaxCreditCarryforwardAxis
= gncma_AlternativeMinimumTaxCreditCarryforwardMember 		      1,700,000us-gaap_TaxCreditCarryforwardAmount
/ us-gaap_TaxCreditCarryforwardAxis
= gncma_AlternativeMinimumTaxCreditCarryforwardMember 		   
Federal              
Operating Loss Carryforwards [Line Items]              
Net operating loss carryforwards $ 320,250,000us-gaap_OperatingLossCarryforwards
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_DomesticCountryMember 		      $ 320,250,000us-gaap_OperatingLossCarryforwards
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_DomesticCountryMember