| **Related Party Transaction (Details) (USD $)** | 3 Months Ended                               | 1 Months Ended                                                                                                                                                  |
|-------------------------------------------------|----------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------|
||
| **Related Party Transaction [Line Items]**      |                                         |                                                                                                                                                            |   |
| Revenue from related party                      | $ 5,283,000us-gaap_RevenueFromRelatedParties | $ 15,780,000us-gaap_RevenueFromRelatedParties                                                                                                                   |   |
| ACS [Member]                                    |                                         |                                                                                                                                                            |   |
| **Related Party Transaction [Line Items]**      |                                         |                                                                                                                                                            |   |
| Payments to related party                       |                                         | 16,200,000us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis= gncma_AlaskaCommunicationsSystemsMember | 6,200,000us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis= gncma_AlaskaCommunicationsSystemsMember |
| Revenue from related party                      |                                         | $ 10,300,000us-gaap_RevenueFromRelatedParties/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis= gncma_AlaskaCommunicationsSystemsMember                      | $ 8,100,000us-gaap_RevenueFromRelatedParties/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis= gncma_AlaskaCommunicationsSystemsMember |

| X                                                                                                                                                                    |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_RelatedPartyTransactionLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                          |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Purchases during the period (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.
+ References
No definition available.
+ Details**Name:**us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.1(e)) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Article 5Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Related Parties -URI http://asc.fasb.org/extlink&oid=16382449Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-07.1(c)) -URI http://asc.fasb.org/extlink&oid=6488393&loc=d3e606610-122999Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 07 -Paragraph b -Subparagraph 1 -Article 6
+ Details**Name:**us-gaap_RevenueFromRelatedParties**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=gncma_AlaskaCommunicationsSystemsMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |