Derivative Instruments - Additional Information (Detail) $ in Thousands, gal in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2016 USD ($) Counterparty	Dec. 31, 2015 USD ($) dekatherm / d Counterparty $ / gal gal
Derivative [Line Items]
Energy Marketing Contract Liabilities, Current	$ 423	$ 433
Propane Swap Agreement [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume \| gal		2.5
Cash Paid On Derivative Settlement	500
Put Option [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume \| gal		2.5
Payments for Derivative Instrument, Financing Activities		$ 143
Cash Received On Derivative Settlement	$ 239
Forward Contracts [Member]
Derivative [Line Items]
Number Of Counterparties With Master Repurchase Agreements \| Counterparty	2	2
Accounts Payable Subject To Master Netting Arrangement		$ 400
Mark To Market Energy Assets [Member] \| Future [Member]
Derivative [Line Items]
Natural Gas Futures Nonmonetary Notional Amount Volume \| dekatherm / d		6,723
Energy Marketing Contract Liabilities, Current		$ 423
Mark To Market Energy Liabilities [Member] \| Future [Member]
Derivative [Line Items]
Energy Marketing Contract Liabilities, Current	$ 423	109
Mark To Market Energy Liabilities [Member] \| Propane Swap Agreement [Member]
Derivative [Line Items]
Energy Marketing Contract Liabilities, Current	0	323
Mark To Market Energy Liabilities [Member] \| Forward Contracts [Member]
Derivative [Line Items]
Energy Marketing Contract Liabilities, Current	$ 0	1
Designated as Hedging Instrument [Member] \| Mark To Market Energy Assets [Member] \| Put Option [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		$ 152
Strike Price 2 [Member] \| Propane Swap Agreement [Member]
Derivative [Line Items]
Strike Price Per Gallon For The Propane Swap Agreements \| $ / gal		0.5950
Strike Price 4 [Member] \| Propane Swap Agreement [Member]
Derivative [Line Items]
Strike Price Per Gallon For The Propane Swap Agreements \| $ / gal		0.5200
Put Option Strike Price 1 [Member] \| Put Option [Member]
Derivative [Line Items]
Derivative, Price Risk Option Strike Price \| $ / gal		0.4950
Put Option Strike Price 2 [Member] \| Put Option [Member]
Derivative [Line Items]
Derivative, Price Risk Option Strike Price \| $ / gal		0.4888
Put Option Strike Price 3 [Member] \| Put Option [Member]
Derivative [Line Items]
Derivative, Price Risk Option Strike Price \| $ / gal		0.4500
Put Option Strike Price 4 [Member] \| Put Option [Member]
Derivative [Line Items]
Derivative, Price Risk Option Strike Price \| $ / gal		0.4200

Accounts Payable Subject To Master Netting Arrangement

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- Definition

Cash Paid On Derivative Settlement

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- Definition

Cash Received On Derivative Settlement

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- Definition

Natural Gas Futures Nonmonetary Notional Amount Volume

+ References

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- Definition

Number Of Counterparties With Master Repurchase Agreements

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- Definition

Strike Price Per Gallon For The Propane Swap Agreements

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- Definition

Fair value, after offset of derivative liability, of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, before offset against an obligation to return collateral under a master netting arrangement. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226008-175313

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226006-175313

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=d3e41678-113959

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Nominal volume used to calculate payments on a derivative instrument.

+ References

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- Definition

The strike price on the price risk option contract such as a put option or a call option.

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- Definition

Current liabilities attributable to energy marketing activities (trading activities). Current energy marketing (trading activities) are when entities engage in both financial and physical trading to increase profits, manage their commodity price risk and enhance system reliability. They may trade electricity, coal, natural gas and oil. These entities typically use a variety of financial instruments, including forward contracts, options and swaps.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.20)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

The cash outflow for derivative instruments during the period, which are classified as financing activities, excluding those designated as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 23
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3505-108585

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