Condensed Consolidated Statements of Income (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Operating Revenues
Regulated energy	$ 109,582us-gaap_RegulatedOperatingRevenue	$ 102,166us-gaap_RegulatedOperatingRevenue
Unregulated energy	60,499us-gaap_UnregulatedOperatingRevenue	84,171us-gaap_UnregulatedOperatingRevenue
Total Operating Revenues	170,081us-gaap_Revenues	186,337us-gaap_Revenues
Operating Expenses
Regulated energy cost of sales	57,129cpk_RegulatedEnergyCostOfSales	54,307cpk_RegulatedEnergyCostOfSales
Unregulated energy and other cost of sales	35,234	61,325
Operations	26,945cpk_Operations	26,626cpk_Operations
Maintenance	2,703us-gaap_MaintenanceCosts	2,148us-gaap_MaintenanceCosts
Depreciation and amortization	6,975	6,635
Other taxes	3,587us-gaap_TaxesOther	3,673us-gaap_TaxesOther
Total Operating Expenses	132,573us-gaap_OperatingExpenses	154,714us-gaap_OperatingExpenses
Operating Income	37,508us-gaap_OperatingIncomeLoss	31,623us-gaap_OperatingIncomeLoss
Other income, net of other expenses	133us-gaap_OtherNonoperatingIncomeExpense	6us-gaap_OtherNonoperatingIncomeExpense
Interest charges	2,448us-gaap_InterestExpense	2,155us-gaap_InterestExpense
Income Before Income Taxes	35,193	29,474
Income taxes	14,084us-gaap_IncomeTaxExpenseBenefit	11,793us-gaap_IncomeTaxExpenseBenefit
Net Income	$ 21,109us-gaap_NetIncomeLoss	$ 17,681us-gaap_NetIncomeLoss
Weighted Average Common Shares Outstanding:
Basic (in shares)	14,604,841	14,487,646
Diluted (in shares)	14,656,310	14,540,151
Earnings Per Share of Common Stock:
Basic (in usd per share)	$ 1.45us-gaap_EarningsPerShareBasic	$ 1.22us-gaap_EarningsPerShareBasic
Diluted (in usd per share)	$ 1.44us-gaap_EarningsPerShareDiluted	$ 1.22us-gaap_EarningsPerShareDiluted
Cash Dividends Declared Per Share of Common Stock (in usd per share)	$ 0.27	$ 0.257

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