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Employee Benefit Plans - Amounts in Accumulated Other Comprehensive Income/Loss and Regulatory Asset (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items] |  |  |
Prior service cost (credit) | $ (59) |  |
Net loss | 778 |  |
Amortization of pre-merger regulatory asset | 769 |  |
Chesapeake Pension Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Prior service cost (credit) | (1) |  |
Net loss | 308 |  |
FPU Pension Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net loss | 332 |  |
Amortization of pre-merger regulatory asset | 761 | 761 | 888
Chesapeake SERP [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Prior service cost (credit) | 19 |  |
Net loss | 64 |  |
Chesapeake Postretirement Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Prior service cost (credit) | (77) |  |
Net loss | 74 |  |
Amortization of pre-merger regulatory asset |  |  |
FPU Medical Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Prior service cost (credit) |  |  |
Net loss |  |  |
Amortization of pre-merger regulatory asset | $ 8 |  |

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- Definition After tax net amount of gain (loss) that are not yet recognized as a component of net periodic benefit cost, and that are recognized as increases (decreases) in other comprehensive income as they arise. + References No definition available. + Details
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- Definition The amounts in accumulated other comprehensive income related to prior service cost or credit expected to be recognized as components of net periodic benefit cost over the next fiscal year that follows the most recent annual statement of financial position presented. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (s) -URI http://asc.fasb.org/extlink&oid=21915506&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 158 -Paragraph 7 -Subparagraph d -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5 -Subparagraph s -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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- Details
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