Employee Benefit Plans - Component of Net Periodic Pension Cost (Benefit) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Components of net periodic cost:
Curtailment gain	$ 0
Expected Amortization Of Pre Merger Regulatory Asset	0
Amortization of pre-merger regulatory asset	769
Chesapeake Pension Plan
Components of net periodic cost:
Interest cost	425	405	458
Expected return on assets	(516)	(486)	(418)
Amortization of prior service cost	0	(1)	(5)
Actuarial (gain) loss	176	322	255
Net periodic pension cost	85	240	290
Amortization of pre-merger regulatory asset	0	0	0
Net periodic postretirement cost	85	240	290
Assumptions
Discount rate	4.25%	3.50%	4.25%
Expected return on plan assets	6.00%	6.00%	6.00%
FPU Pension Plan
Components of net periodic cost:
Interest cost	2,613	2,367	2,577
Expected return on assets	(3,089)	(2,866)	(2,627)
Amortization of prior service cost	0	0	0
Actuarial (gain) loss	8	330	196
Net periodic pension cost	(468)	(169)	146
Amortization of pre-merger regulatory asset	761	761	761
Net periodic postretirement cost	293	592	907
Assumptions
Discount rate	4.75%	3.75%	4.50%
Expected return on plan assets	7.00%	7.00%	7.00%
Chesapeake SERP
Components of net periodic cost:
Interest cost	92	81	90
Amortization of prior service cost	19	19	19
Actuarial (gain) loss	47	64	46
Amortization of pre-merger regulatory asset	0
Net periodic postretirement cost	158	164	155
Assumptions
Discount rate	4.25%	3.50%	4.25%
Chesapeake Postretirement Plan
Components of net periodic cost:
Service cost	0	0	0
Interest cost	39	47	55
Amortization of prior service cost	(77)	(77)	(77)
Actuarial (gain) loss	55	74	73
Net periodic pension cost	17	44	51
Curtailment gain		0	0
Expected Amortization Of Pre Merger Regulatory Asset		0	0
Amortization of pre-merger regulatory asset	0
Net periodic postretirement cost	17	44	51
Assumptions
Discount rate	4.25%	3.50%	4.25%
FPU Medical Plan
Components of net periodic cost:
Service cost	0	0	1
Interest cost	69	63	79
Amortization of prior service cost	0	0	0
Actuarial (gain) loss	0	0	0
Net periodic pension cost	69	63	80
Curtailment gain	0	0	(892)
Amortization of pre-merger regulatory asset	8	8	8
Net periodic postretirement cost	$ 77	$ 71	$ (804)
Assumptions
Discount rate	4.75%	3.75%	4.50%

Amortization of pre-merger regulatory asset.

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- Definition

Expected amortization of pre merger regulatory asset.

+ References

No definition available.

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- Definition

Net periodic cost benefit.

+ References

No definition available.

+ Details

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- Definition

The amount of the prior service cost or credit recognized in net periodic benefit cost relating to benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation.

+ References

+ Details

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- Definition

The interest rate used to adjust for the time value of money.

+ References

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- Definition

An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 30

-Glossary Expected Long-Term Rate of Return on Plan Assets

-URI http://asc.fasb.org/extlink&oid=6512013

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-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (k)(3)

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- Definition

An amount calculated as a basis for determining the extent of delayed recognition of the effects of changes in the fair value of assets. The expected return on plan assets is determined based on the expected long-term rate of return on plan assets and the market-related value of plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 30

-Glossary Expected Return on Plan Assets

-URI http://asc.fasb.org/extlink&oid=6512136

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 60

-Glossary Expected Return on Plan Assets

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-Topic 715

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-Section 50

-Paragraph 1

-Subparagraph (h)(3)

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- Definition

Amount included in accumulated other comprehensive income (AOCI) related to gain (loss) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position.

+ References

No definition available.

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- Definition

The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

+ References

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- Definition

The total amount of net periodic benefit cost for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments.

+ References

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- Definition

The amount of net gain (loss) recognized in net periodic benefit cost as a result of an event that significantly reduces the expected years of future service of present employees or eliminates for a significant number of employees the accrual of defined benefits for some or all of their future services.

+ 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 (h)(7)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Plan Curtailment

-URI http://asc.fasb.org/extlink&oid=6520938

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

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- Definition

The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.

+ 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 (h)(1)

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Service Cost (Component of Net Periodic Pension Cost)

-URI http://asc.fasb.org/extlink&oid=6525008

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-Publisher FASB

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-Topic 715

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-Subparagraph (a)(1)

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