| **Receivables and Allowance for Doubtful Receivables (Receivables by Type) (Details) (USD $)In Thousands, unless otherwise specified** | Dec. 31, 2014                                                                                                                                              | Dec. 31, 2013                                                                                                                                              |
|----------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------|
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                       |                                                                                                                                                       |                                                                                                                                                       |
| Receivables                                                                                                                            | $ 212,441us-gaap_AccountsReceivableGrossCurrent                                                                                                            | $ 228,372us-gaap_AccountsReceivableGrossCurrent                                                                                                            |
| Trade Accounts Receivable                                                                                                              |                                                                                                                                                       |                                                                                                                                                       |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                       |                                                                                                                                                       |                                                                                                                                                       |
| Receivables                                                                                                                            | 209,811us-gaap_AccountsReceivableGrossCurrent/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis= us-gaap_TradeAccountsReceivableMember | 225,689us-gaap_AccountsReceivableGrossCurrent/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis= us-gaap_TradeAccountsReceivableMember |
| Employee Receivable                                                                                                                    |                                                                                                                                                       |                                                                                                                                                       |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                       |                                                                                                                                                       |                                                                                                                                                       |
| Receivables                                                                                                                            | 801us-gaap_AccountsReceivableGrossCurrent/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis= gncma_EmployeeReceivableMember            | 1,037us-gaap_AccountsReceivableGrossCurrent/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis= gncma_EmployeeReceivableMember          |
| Other Receivable                                                                                                                       |                                                                                                                                                       |                                                                                                                                                       |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                       |                                                                                                                                                       |                                                                                                                                                       |
| Receivables                                                                                                                            | $ 1,829us-gaap_AccountsReceivableGrossCurrent/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis= gncma_OtherReceivableMember           | $ 1,646us-gaap_AccountsReceivableGrossCurrent/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis= gncma_OtherReceivableMember           |

| X                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_AccountsNotesAndLoansReceivableLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amounts due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer) for goods or services (including trade receivables) that have been delivered or sold in the normal course of business.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.3) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 3 -Subparagraph a, b -Article 5
+ Details**Name:**us-gaap_AccountsReceivableGrossCurrent**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                           |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=gncma_EmployeeReceivableMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                        |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=gncma_OtherReceivableMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_TradeAccountsReceivableMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |