Annual report pursuant to Section 13 and 15(d)

Receivables and Allowance for Doubtful Receivables (Receivables by Type) (Details)

v2.4.1.9
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