Derivative Instruments - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Accounts Receivable Subject to Master Netting Arrangement	$ 3,264	$ 3,834
Accounts Payable Subject To Master Netting Arrangement	3,264	3,834
Other Payables to Broker-Dealers and Clearing Organizations	(335)
Other Receivables from Broker-Dealers and Clearing Organizations		2,810
Energy Marketing Contracts Assets, Current	9,221	13,165
Energy Marketing Contract Liabilities, Current	(6,798)	(14,871)
Derivative, Amount of Hedged Item	6	212
Hedging Liability [Member] \| Natural Gas Futures [Member]
Derivative [Line Items]
Energy Marketing Contract Liabilities, Current	(3,533)	(8,705)
Designated as Hedging Instrument [Member] \| Mark To Market Energy Assets [Member] \| Put Option [Member]
Derivative [Line Items]
Energy Marketing Contracts Assets, Current	0	71
Designated as Hedging Instrument [Member] \| Mark To Market Energy Assets [Member] \| Natural Gas Futures [Member]
Derivative [Line Items]
Energy Marketing Contracts Assets, Current	7,055	9,059
Designated as Hedging Instrument [Member] \| Mark To Market Energy Assets [Member] \| Propane Swap Agreement [Member]
Derivative [Line Items]
Energy Marketing Contracts Assets, Current	44	11
Designated as Hedging Instrument [Member] \| Mark-to-market energy liabilities [Member] \| Propane Swap Agreement [Member]
Derivative [Line Items]
Energy Marketing Contract Liabilities, Current	(627)	(1,604)
Not Designated as Hedging Instrument [Member] \| Mark To Market Energy Assets [Member] \| Natural Gas Futures [Member]
Derivative [Line Items]
Energy Marketing Contracts Assets, Current	2,122	4,024
Not Designated as Hedging Instrument [Member] \| Mark-to-market energy liabilities [Member] \| Natural Gas Futures [Member]
Derivative [Line Items]
Energy Marketing Contract Liabilities, Current	(2,638)	(4,562)
Gross [Member]
Derivative [Line Items]
Accounts Receivable Subject to Master Netting Arrangement	8,832	12,368
Accounts Payable Subject To Master Netting Arrangement	15,906	24,741
Net [Member]
Derivative [Line Items]
Accounts Receivable Subject to Master Netting Arrangement	5,568	8,534
Accounts Payable Subject To Master Netting Arrangement	$ 12,642	$ 20,907

Accounts Payable Subject To Master Netting Arrangement

No definition available.

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- Definition

Accounts Receivable Subject to Master Netting Arrangement

+ References

No definition available.

+ Details

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- Definition

Amount of hedged item in hedging relationship. Excludes hedged asset or liability.

+ References

No definition available.

+ Details

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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.

+ References

No definition available.

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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://fasb.org/us-gaap/role/ref/legacyRef
-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

+ Details

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- Definition

Carrying amount as of the balance sheet date of the asset arising from energy trading activities that involves the purchase and sale of energy under forward contracts at fixed and variable prices and the buying and selling of financial energy contracts that include exchange futures and options and over the counter options and swaps, which are expected to be converted into cash or otherwise disposed of within a year or the normal operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Amount of other payables due to broker-dealers or clearing organizations.

+ References

No definition available.

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- Definition

Amount of other receivables due from broker-dealers or clearing organizations.

+ References

No definition available.

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