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Derivative Instruments - Additional Information (Detail) $ in Thousands, gal in Millions, Mcf in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 USD ($) gal Mcf | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($)
Derivative [Line Items] |  |  |
Derivative, Amount of Hedged Item | $ 212 | $ 0 |
Other Receivables from Broker-Dealers and Clearing Organizations | 2,810 | 6,300 |
Energy Marketing Contract Liabilities, Current | 14,871 | 6,247 |
Accounts Payable Subject To Master Netting Arrangement | 3,834 | 2,391 |
Derivative assets, at fair value | 13,165 | 1,286 |
Unrealized Gain (Loss) on Derivatives | (7,703) | (3,195) | $ (45)
Hedging Liability [Member] | Natural Gas Futures [Member] |  |  |
Derivative [Line Items] |  |  |
Energy Marketing Contract Liabilities, Current | $ 8,705 |  |
Not Designated as Hedging Instrument [Member] | Natural Gas Futures [Member] |  |  |
Derivative [Line Items] |  |  |
Derivative, Nonmonetary Notional Amount, Volume | Mcf | 3.8 |  |
Not Designated as Hedging Instrument [Member] | Mark To Market Energy Assets | Natural Gas Futures [Member] |  |  |
Derivative [Line Items] |  |  |
Derivative assets, at fair value | $ 4,024 |  |
Not Designated as Hedging Instrument [Member] | Mark To Market Energy Assets | Propane Swap Agreement |  |  |
Derivative [Line Items] |  |  |
Derivative assets, at fair value |  | 13 |
Not Designated as Hedging Instrument [Member] | Mark-to-market energy liabilities | Natural Gas Futures [Member] |  |  |
Derivative [Line Items] |  |  |
Energy Marketing Contract Liabilities, Current | 4,562 | 5,776 |
Derivatives designated as fair value hedges | Mark To Market Energy Assets | Natural Gas Futures [Member] |  |  |
Derivative [Line Items] |  |  |
Derivative assets, at fair value | 9,059 | 92 |
Derivatives designated as fair value hedges | Mark To Market Energy Assets | Put Option |  |  |
Derivative [Line Items] |  |  |
Derivative assets, at fair value | 71 |  |
Derivatives designated as fair value hedges | Mark To Market Energy Assets | Propane Swap Agreement |  |  |
Derivative [Line Items] |  |  |
Derivative assets, at fair value | 11 | 1,181 |
Derivatives designated as fair value hedges | Mark-to-market energy liabilities | Propane Swap Agreement |  |  |
Derivative [Line Items] |  |  |
Energy Marketing Contract Liabilities, Current | 0 | 469 |
Sharp Energy Inc [Member] |  |  |
Derivative [Line Items] |  |  |
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months | $ 1,235 |  |
Sharp Energy Inc [Member] | Put Option |  |  |
Derivative [Line Items] |  |  |
Derivative, Nonmonetary Notional Amount, Volume | gal | 0.3 |  |
PESCO [Member] |  |  |
Derivative [Line Items] |  |  |
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months | $ 1,534 |  |
PESCO [Member] | Natural Gas Futures [Member] |  |  |
Derivative [Line Items] |  |  |
Derivative, Nonmonetary Notional Amount, Volume | Mcf | 14.4 |  |
2017 [Member] | Derivatives designated as fair value hedges | Mark-to-market energy liabilities | Propane Swap Agreement |  |  |
Derivative [Line Items] |  |  |
Energy Marketing Contract Liabilities, Current | $ 1,604 | 2 |
Other Comprehensive Income (Loss) | Derivatives designated as fair value hedges | Natural Gas Futures [Member] |  |  |
Derivative [Line Items] |  |  |
Unrealized Gain (Loss) on Derivatives | 532 | (1,476) | 222
Other Comprehensive Income (Loss) | Derivatives designated as fair value hedges | Natural Gas Swaps [Member] |  |  |
Derivative [Line Items] |  |  |
Unrealized Gain (Loss) on Derivatives | 200 | 986 | 0
Other Comprehensive Income (Loss) | Derivatives designated as fair value hedges | Propane Swap Agreement |  |  |
Derivative [Line Items] |  |  |
Unrealized Gain (Loss) on Derivatives | (2,773) | 487 | 1,016
Cost of Sales [Member] | Not Designated as Hedging Instrument [Member] | Future [Member] |  |  |
Derivative [Line Items] |  |  |
Unrealized Gain (Loss) on Derivatives | (3,189) | (3,633) | (541)
Cost of Sales [Member] | Not Designated as Hedging Instrument [Member] | Propane Swap Agreement |  |  |
Derivative [Line Items] |  |  |
Derivative, Gain (Loss) on Derivative, Net | (13) | 8 | 7
Cost of Sales [Member] | Derivatives designated as fair value hedges | Natural Gas Swaps [Member] |  |  |
Derivative [Line Items] |  |  |
Unrealized Gain (Loss) on Derivatives |  |  | 0
Cost of Sales [Member] | Derivatives designated as fair value hedges | Future [Member] |  |  |
Derivative [Line Items] |  |  |
Unrealized Gain (Loss) on Derivatives |  |  | 345
Cost of Sales [Member] | Derivatives designated as fair value hedges | Propane Swap Agreement |  |  |
Derivative [Line Items] |  |  |
Derivative, Gain (Loss) on Derivative, Net | (647) | 1,607 | (364)
Inventories [Member] | Not Designated as Hedging Instrument [Member] | Natural Gas Swaps [Member] |  |  |
Derivative [Line Items] |  |  |
Derivative, Gain (Loss) on Derivative, Net | $ 0 | $ 1 | $ 0

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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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