Net Property and Equipment (Consideration Transferred) (Details) $ in Thousands	Nov. 30, 2016 USD ($)
Allocation of consideration to assets acquired and liabilities assumed:
Property and equipment	$ 49,794
Deferred taxes	(12,211)
Deferred revenue	(3,815)
Total consideration	$ 33,768

Asset Acquisition, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Deferred Revenue

No definition available.

Name:	gncma_AssetAcquisitionRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedCurrentLiabilitiesDeferredRevenue
Namespace Prefix:	gncma_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant