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Industry Segments Data (Narrative) (Details) (USD $)
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12 Months Ended | ||
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Dec. 31, 2014
segment
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Dec. 31, 2013
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Dec. 31, 2012
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| Segment Reporting Information [Line Items] | |||
| Number of reportable segments | 2us-gaap_NumberOfReportableSegments | ||
| Percentage of long-lived assets not in US | 82.00%gncma_SegmentReportingInformationPercentageofLongLivedAssetsNotLocatedinCountryofOrigin | ||
| Revenues | $ 910,198,000us-gaap_Revenues | $ 811,648,000us-gaap_Revenues | $ 710,181,000us-gaap_Revenues |
| Wireless | |||
| Segment Reporting Information [Line Items] | |||
| Equipment subsidy |
17,300,000gncma_EquipmentSubsidy / us-gaap_StatementBusinessSegmentsAxis = gncma_WirelessSegmentMember |
12,200,000gncma_EquipmentSubsidy / us-gaap_StatementBusinessSegmentsAxis = gncma_WirelessSegmentMember |
23,200,000gncma_EquipmentSubsidy / us-gaap_StatementBusinessSegmentsAxis = gncma_WirelessSegmentMember |
| Revenues |
269,977,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = gncma_WirelessSegmentMember |
197,218,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = gncma_WirelessSegmentMember |
124,745,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = gncma_WirelessSegmentMember |
| Customer Concentration Risk | |||
| Segment Reporting Information [Line Items] | |||
| Concentration Risk, Percentage |
6.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember |
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| Customer Concentration Risk | Sales Revenue, Net | Wireless and Wireline | |||
| Segment Reporting Information [Line Items] | |||
| Revenues |
$ 108,300,000us-gaap_Revenues / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = gncma_WirelessandWirelineMember |
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| Concentration Risk, Percentage |
12.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = gncma_WirelessandWirelineMember |
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- Definition
Equipment Subsidy No definition available.
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- Definition
Segment Reporting Information, Percentage of Long-Lived Assets Not Located in Country of Origin No definition available.
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- Definition
For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements. No definition available.
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- Definition
Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss). Reference 1: http://www.xbrl.org/2003/role/presentationRef
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