| **Long Term Debt (Schedule of Redemption Prices) (Details)** | 12 Months Ended |
|--------------------------------------------------------------|-----------------|
||
| 2021 Notes [Member]                                          |            |
| **Debt Instrument [Line Items]**                             |            |
| 2016                                                         | 103.375%        |
| 2017                                                         | 102.25%         |
| 2018                                                         | 101.125%        |
| 2019 and thereafter                                          | 100.00%         |
| 2019 Notes [Member]                                          |            |
| **Debt Instrument [Line Items]**                             |            |
| 2014                                                         | 104.313%        |
| 2015                                                         | 102.875%        |
| 2016                                                         | 101.438%        |
| 2017 and thereafter                                          | 100.00%         |

| X                                                                                                                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Redemption price in percentage in 2018 after the redemption date.
+ References
No definition available.
+ Details**Name:**gncma_RedemptinPriceInTwentyEighteen**Namespace Prefix:**gncma_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Redemption price in percentage in 2015 after the redemption date.
+ References
No definition available.
+ Details**Name:**gncma_RedemptinPriceInTwentyFifteen**Namespace Prefix:**gncma_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Redemption price in percentage in 2014 after the redemption date.
+ References
No definition available.
+ Details**Name:**gncma_RedemptinPriceInTwentyFourteen**Namespace Prefix:**gncma_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                             |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Redemption price in percentage in 2019 and thereafter after the redemption date.
+ References
No definition available.
+ Details**Name:**gncma_RedemptinPriceInTwentyNineteenAndThereafter**Namespace Prefix:**gncma_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                   |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Redemption price in percentage in 2017 after the redemption date.
+ References
No definition available.
+ Details**Name:**gncma_RedemptinPriceInTwentySeventeen**Namespace Prefix:**gncma_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Redemption price in percentage in 2017 and thereafter after the redemption date.
+ References
No definition available.
+ Details**Name:**gncma_RedemptinPriceInTwentySeventeenAndThereafter**Namespace Prefix:**gncma_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Redemption price in percentage in 2016 after the redemption date.
+ References
No definition available.
+ Details**Name:**gncma_RedemptinPriceInTwentySixteen**Namespace Prefix:**gncma_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                           |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DebtInstrumentLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |