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Consolidated Statements of Stockholders' Equity Consolidated Statements of Stockholders' Equity (Parenthetical) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Statement of Stockholders' Equity [Abstract]      
Shares Held In Trust For Deferred Compensation Plan 53,125cpk_SharesHeldInTrustForDeferredCompensationPlan 51,743cpk_SharesHeldInTrustForDeferredCompensationPlan 50,192cpk_SharesHeldInTrustForDeferredCompensationPlan
Dividends Declared $ 1.067us-gaap_CommonStockDividendsPerShareDeclared $ 1.013us-gaap_CommonStockDividendsPerShareDeclared $ 0.96us-gaap_CommonStockDividendsPerShareDeclared
Shares Issued Under Performance Incentive Plan Withheld For Employee Taxes 12,687cpk_SharesIssuedUnderPerformanceIncentivePlanWithheldForEmployeeTaxes 15,616.5cpk_SharesIssuedUnderPerformanceIncentivePlanWithheldForEmployeeTaxes 8,505cpk_SharesIssuedUnderPerformanceIncentivePlanWithheldForEmployeeTaxes