Annual report pursuant to Section 13 and 15(d)

Financial Instruments (Assets measured at fair value on a recurring basics) (Details)

v2.4.1.9
Financial Instruments (Assets measured at fair value on a recurring basics) (Details) (Fair Value, Inputs, Level 1, USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Fair Value, Inputs, Level 1
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Deferred compensation plan assets (mutual funds) $ 2,068gncma_DeferredCompensationAssetsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member 		$ 2,183gncma_DeferredCompensationAssetsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Total assets at fair value $ 2,068us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member 		$ 2,183us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member