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Employee Benefit Plans - Schedule of Amounts Not Yet Reflected in Net Periodic Benefit Cost and Included in Accumulated Other Comprehensive Income Loss or Regulatory Assets (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified | Dec. 31, 2012
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Defined Benefit Plan Disclosure [Line Items] |
Income tax benefits | $ 3.3

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- Definition Accumulated Other Comprehensive Income Loss Tax Effect + References No definition available. + Details
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Namespace Prefix: | cpk_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration