Annual report pursuant to Section 13 and 15(d)

Receivables and Allowance for Doubtful Receivables (Narrative) (Details)

v2.4.1.9
Receivables and Allowance for Doubtful Receivables (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2014
Dec. 31, 2013
USF Program      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Revenue support from regulatory agency, percentage 18.00%gncma_PublicUtilitiesRevenueSupportFromRegulatoryAgencyPercentage
/ us-gaap_RegulatoryAgencyAxis
= gncma_UsfProgramMember
19.00%gncma_PublicUtilitiesRevenueSupportFromRegulatoryAgencyPercentage
/ us-gaap_RegulatoryAgencyAxis
= gncma_UsfProgramMember
18.00%gncma_PublicUtilitiesRevenueSupportFromRegulatoryAgencyPercentage
/ us-gaap_RegulatoryAgencyAxis
= gncma_UsfProgramMember
Receivables net current   $ 109.6us-gaap_ReceivablesNetCurrent
/ us-gaap_RegulatoryAgencyAxis
= gncma_UsfProgramMember
$ 124.3us-gaap_ReceivablesNetCurrent
/ us-gaap_RegulatoryAgencyAxis
= gncma_UsfProgramMember
Rural Health Care Division      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Proceeds from regulatory agency $ 1.6gncma_ProceedsfromRegulatoryAgency
/ us-gaap_RegulatoryAgencyAxis
= gncma_RuralHealthCareDivisionMember