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Derivative Instruments - Outstanding Trading Contracts (Detail) (Forward Contracts)
Dec. 31, 2014
gal
Dec. 31, 2013
gal
Revenue    
Derivative [Line Items]    
Quantity in Gallons 4,200,000cpk_QuantityInGallons
/ us-gaap_DerivativeByNatureAxis
= us-gaap_ForwardContractsMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesMember		 1,892,000cpk_QuantityInGallons
/ us-gaap_DerivativeByNatureAxis
= us-gaap_ForwardContractsMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesMember
Weighted Average Contract Prices 0.6714cpk_WeightedAverageContractPrices
/ us-gaap_DerivativeByNatureAxis
= us-gaap_ForwardContractsMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesMember		 1.2786cpk_WeightedAverageContractPrices
/ us-gaap_DerivativeByNatureAxis
= us-gaap_ForwardContractsMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesMember
Purchase    
Derivative [Line Items]    
Quantity in Gallons 4,201,000cpk_QuantityInGallons
/ us-gaap_DerivativeByNatureAxis
= us-gaap_ForwardContractsMember
/ us-gaap_IncomeStatementLocationAxis
= cpk_PurchaseMember		 1,991,000cpk_QuantityInGallons
/ us-gaap_DerivativeByNatureAxis
= us-gaap_ForwardContractsMember
/ us-gaap_IncomeStatementLocationAxis
= cpk_PurchaseMember
Weighted Average Contract Prices 0.6416cpk_WeightedAverageContractPrices
/ us-gaap_DerivativeByNatureAxis
= us-gaap_ForwardContractsMember
/ us-gaap_IncomeStatementLocationAxis
= cpk_PurchaseMember		 1.2444cpk_WeightedAverageContractPrices
/ us-gaap_DerivativeByNatureAxis
= us-gaap_ForwardContractsMember
/ us-gaap_IncomeStatementLocationAxis
= cpk_PurchaseMember
Minimum | Revenue    
Derivative [Line Items]    
Estimated Market Prices 0.5400cpk_EstimatedMarketPrices
/ us-gaap_DerivativeByNatureAxis
= us-gaap_ForwardContractsMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		 0.9900cpk_EstimatedMarketPrices
/ us-gaap_DerivativeByNatureAxis
= us-gaap_ForwardContractsMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Minimum | Purchase    
Derivative [Line Items]    
Estimated Market Prices 0.4700cpk_EstimatedMarketPrices
/ us-gaap_DerivativeByNatureAxis
= us-gaap_ForwardContractsMember
/ us-gaap_IncomeStatementLocationAxis
= cpk_PurchaseMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		 0.9411cpk_EstimatedMarketPrices
/ us-gaap_DerivativeByNatureAxis
= us-gaap_ForwardContractsMember
/ us-gaap_IncomeStatementLocationAxis
= cpk_PurchaseMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Maximum | Revenue    
Derivative [Line Items]    
Estimated Market Prices 0.7900cpk_EstimatedMarketPrices
/ us-gaap_DerivativeByNatureAxis
= us-gaap_ForwardContractsMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		 1.4750cpk_EstimatedMarketPrices
/ us-gaap_DerivativeByNatureAxis
= us-gaap_ForwardContractsMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Maximum | Purchase    
Derivative [Line Items]    
Estimated Market Prices 1.3176cpk_EstimatedMarketPrices
/ us-gaap_DerivativeByNatureAxis
= us-gaap_ForwardContractsMember
/ us-gaap_IncomeStatementLocationAxis
= cpk_PurchaseMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		 1.4600cpk_EstimatedMarketPrices
/ us-gaap_DerivativeByNatureAxis
= us-gaap_ForwardContractsMember
/ us-gaap_IncomeStatementLocationAxis
= cpk_PurchaseMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember