Annual report pursuant to Section 13 and 15(d)

Income Taxes (Statutory tax rate impact on Income tax expense) (Details)

v2.4.1.9
Income Taxes (Statutory tax rate impact on Income tax expense) (Details) (USD $)
In Thousands, unless otherwise specified
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
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]              
Expected statutory tax expense         $ 24,246us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate $ 14,939us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate $ 7,437us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate
Impact of non-controlling interest attributable to non-tax paying entity         (18,255)us-gaap_IncomeTaxReconciliationMinorityInterestIncomeExpense (7,977)us-gaap_IncomeTaxReconciliationMinorityInterestIncomeExpense 0us-gaap_IncomeTaxReconciliationMinorityInterestIncomeExpense
State income taxes, net of federal expense         948us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes 1,690us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes 1,770us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes
Income tax effect of nondeductible entertainment expenses         1,125us-gaap_IncomeTaxReconciliationNondeductibleExpenseMealsAndEntertainment 1,045us-gaap_IncomeTaxReconciliationNondeductibleExpenseMealsAndEntertainment 777us-gaap_IncomeTaxReconciliationNondeductibleExpenseMealsAndEntertainment
Income tax effect of nondeductible lobbying expenses         425gncma_IncomeTaxReconciliationNondeductibleExpenseLobbying 369gncma_IncomeTaxReconciliationNondeductibleExpenseLobbying 298gncma_IncomeTaxReconciliationNondeductibleExpenseLobbying
Income tax effect of nondeductible officer compensation         1,351us-gaap_IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost 824us-gaap_IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost 1,718us-gaap_IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost
Other, net         189us-gaap_IncomeTaxReconciliationNondeductibleExpenseOther 67us-gaap_IncomeTaxReconciliationNondeductibleExpenseOther 88us-gaap_IncomeTaxReconciliationNondeductibleExpenseOther
Income Tax Expense (Benefit), Total $ 1,400us-gaap_IncomeTaxExpenseBenefit $ 5,078us-gaap_IncomeTaxExpenseBenefit $ 2,355us-gaap_IncomeTaxExpenseBenefit $ 1,196us-gaap_IncomeTaxExpenseBenefit $ 10,029us-gaap_IncomeTaxExpenseBenefit $ 10,957us-gaap_IncomeTaxExpenseBenefit $ 12,088us-gaap_IncomeTaxExpenseBenefit