| **Net Property and Equipment in Service (Details) (USD $)In Thousands, unless otherwise specified** | Dec. 31, 2012 | Dec. 31, 2011 |
|-----------------------------------------------------------------------------------------------------|---------------|---------------|
| **Property, Plant and Equipment [Line Items]**                                                      |          |          |
| Property, Plant and Equipment, Gross                                                                | $ 1,773,887   | $ 1,672,846   |
| Accumulated Depreciation Property Plant And Equipment                                               | 901,398       | 798,794       |
| Accumulated Amortization Property Plant And Equipment                                               | 34,242        | 24,931        |
| Net property and equipment in service                                                               | 838,247       | 849,121       |
| Land and buildings                                                                                  |          |          |
| **Property, Plant and Equipment [Line Items]**                                                      |          |          |
| Property, Plant and Equipment, Gross                                                                | 56,507        | 47,133        |
| Telephony transmission equipment and distribution facilities                                        |          |          |
| **Property, Plant and Equipment [Line Items]**                                                      |          |          |
| Property, Plant and Equipment, Gross                                                                | 798,932       | 752,083       |
| Cable transmission equipment and distribution facilities                                            |          |          |
| **Property, Plant and Equipment [Line Items]**                                                      |          |          |
| Property, Plant and Equipment, Gross                                                                | 155,122       | 141,400       |
| Support equipment and systems                                                                       |          |          |
| **Property, Plant and Equipment [Line Items]**                                                      |          |          |
| Property, Plant and Equipment, Gross                                                                | 216,495       | 202,785       |
| Transportation equipment                                                                            |          |          |
| **Property, Plant and Equipment [Line Items]**                                                      |          |          |
| Property, Plant and Equipment, Gross                                                                | 9,184         | 8,269         |
| Property and equipment under capital leases                                                         |          |          |
| **Property, Plant and Equipment [Line Items]**                                                      |          |          |
| Property, Plant and Equipment, Gross                                                                | 104,251       | 102,972       |
| Customer premise equipment                                                                          |          |          |
| **Property, Plant and Equipment [Line Items]**                                                      |          |          |
| Property, Plant and Equipment, Gross                                                                | 142,176       | 134,207       |
| Fiber optic cable systems                                                                           |          |          |
| **Property, Plant and Equipment [Line Items]**                                                      |          |          |
| Property, Plant and Equipment, Gross                                                                | $ 291,220     | $ 283,997     |

| X                                                                                                                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The cumulative amount of amortization (related to property, plant and equipment, but not including land) that has been recognized in the income statement.
+ References
No definition available.
+ Details**Name:**gncma_AccumulatedAmortizationPropertyPlantAndEquipment**Namespace Prefix:**gncma_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The cumulative amount of depreciation that has been recognized in the income statement.
+ References
No definition available.
+ Details**Name:**gncma_AccumulatedDepreciationPropertyPlantAndEquipment**Namespace Prefix:**gncma_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Tangible assets that are held by an entity and have been placed into service for use in the production or supply of goods and services, for rental to others, or for administrative purposes and that are expected to provide economic benefit for more than one year; net of accumulated depreciation. Examples include land, buildings, and production equipment. Excludes Construction in Progress.
+ References
No definition available.
+ Details**Name:**gncma_PropertyAndEquipmentInServiceNetOfDepreciation**Namespace Prefix:**gncma_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Gross amount of long-lived physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 5 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.13) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682
+ Details**Name:**us-gaap_PropertyPlantAndEquipmentGross**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                      |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_PropertyPlantAndEquipmentLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |