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