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Inventories (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Inventory Disclosures [Line Items]    
Consignment inventory $ 26.4bgc_ConsignmentInventory $ 32.5bgc_ConsignmentInventory
Venezuela [Member]    
Inventory Disclosures [Line Items]    
Inventory, lower of cost or market charges recognized $ 9.5bgc_InventoryLowerofCostorMarketChargesRecognized
/ us-gaap_StatementGeographicalAxis
= country_VE		  
UNITED STATES AND CANADA [Member]    
Inventory Disclosures [Line Items]    
Consignment inventory, percentage 83.00%bgc_PercentageOfConsignmentInventory
/ us-gaap_StatementGeographicalAxis
= bgc_UnitedStatesAndCanadaMember		 87.00%bgc_PercentageOfConsignmentInventory
/ us-gaap_StatementGeographicalAxis
= bgc_UnitedStatesAndCanadaMember