Derivative Instruments - Additional Information (Detail) gal in Thousands, Mcf in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / gal gal Mcf	Dec. 31, 2016 USD ($) $ / gal gal	Dec. 31, 2015 USD ($) $ / gal gal
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | Mcf	2,900
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ 520
Energy Marketing Contract Liabilities, Current	6,247	$ 773
Accounts Payable Subject To Master Netting Arrangement	2,391	1,431
Derivative assets, at fair value	1,286	823
Unrealized Gain (Loss) on Derivatives	(3,195)	(45)	$ 474
Put Option
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | gal			2,500
Payment to purchase call options			$ 143
Cash Received On Derivative Settlement			$ 239
Propane Swap Agreement
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | gal			2,500
Cash Paid On Derivative Settlement			$ 484
Hedging Liability [Member] | Natural Gas Swaps [Member]
Derivative [Line Items]
Energy Marketing Contract Liabilities, Current	(469)
Not Designated as Hedging Instrument [Member] | Mark To Market Energy Assets | Propane Swap Agreement
Derivative [Line Items]
Derivative assets, at fair value	13	8
Not Designated as Hedging Instrument [Member] | Mark-to-market energy liabilities | Natural Gas Futures [Member]
Derivative [Line Items]
Energy Marketing Contract Liabilities, Current	5,776	773
Derivatives designated as fair value hedges | Mark To Market Energy Assets | Natural Gas Futures [Member]
Derivative [Line Items]
Derivative assets, at fair value	92	113
Derivatives designated as fair value hedges | Mark To Market Energy Assets | Put Option
Derivative [Line Items]
Derivative assets, at fair value	0	9
Derivatives designated as fair value hedges | Mark To Market Energy Assets | Propane Swap Agreement
Derivative [Line Items]
Derivative assets, at fair value	1,181	693
Derivatives designated as fair value hedges | Mark-to-market energy liabilities | Propane Swap Agreement
Derivative [Line Items]
Energy Marketing Contract Liabilities, Current	$ 469	$ 0
Put Option Strike Price 1 [Member] | Put Option
Derivative [Line Items]
Strike price of put option | $ / gal		0.4950
Put Option Strike Price 2 [Member] | Put Option
Derivative [Line Items]
Strike price of put option | $ / gal			0.4888
Put Option Strike Price 3 [Member] | Put Option
Derivative [Line Items]
Strike price of put option | $ / gal			0.4500
Put Option Strike Price 4 [Member] | Put Option
Derivative [Line Items]
Strike price of put option | $ / gal			0.4200
Strike Price 1 [Member] | Propane Swap Agreement
Derivative [Line Items]
Strike Price Per Gallon For The Propane Swap Agreements | $ / gal			0.5200
Strike Price 2 [Member] | Propane Swap Agreement
Derivative [Line Items]
Strike Price Per Gallon For The Propane Swap Agreements | $ / gal			0.5950
Sharp Energy Inc [Member] | Put Option
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | gal		630
Strike price of put option | $ / gal		0.5650
Payment to purchase call options		$ 33
PESCO [Member] | Natural Gas Futures [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | Mcf	17,200
2017 [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | gal	4,900
2017 [Member] | Natural Gas Swaps [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | Mcf	591
2017 [Member] | Propane Swap Agreement
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | gal	7,700
Derivative, Cash Received on Hedge	$ 440
Volume settled on hedges | gal	1,470
2017 [Member] | Derivatives designated as fair value hedges | Mark-to-market energy liabilities | Propane Swap Agreement
Derivative [Line Items]
Energy Marketing Contract Liabilities, Current	$ 2	$ 0
2017 [Member] | Strike Price 1 [Member] | Propane Swap Agreement
Derivative [Line Items]
Strike Price Per Gallon For The Propane Swap Agreements | $ / gal	0.59
2016 [Member] | Propane Swap Agreement
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | gal	0
Derivative, Cash Received on Hedge	$ (663)
2016 [Member] | Strike Price 1 [Member] | Propane Swap Agreement
Derivative [Line Items]
Strike Price Per Gallon For The Propane Swap Agreements | $ / gal		0.5225
2016 [Member] | Strike Price 2 [Member] | Propane Swap Agreement
Derivative [Line Items]
Strike Price Per Gallon For The Propane Swap Agreements | $ / gal		0.5650
Other Comprehensive Income (Loss) | Derivatives designated as fair value hedges | Natural Gas Futures [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(1,476)	$ 222	$ 109
Other Comprehensive Income (Loss) | Derivatives designated as fair value hedges | Natural Gas Swaps [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	986	0	0
Other Comprehensive Income (Loss) | Derivatives designated as fair value hedges | Propane Swap Agreement
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	487	1,016	(323)
Cost of Sales [Member] | Not Designated as Hedging Instrument [Member] | Future [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(3,633)	(541)	0
Cost of Sales [Member] | Not Designated as Hedging Instrument [Member] | Propane Swap Agreement
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	8	7	18
Cost of Sales [Member] | Derivatives designated as fair value hedges | Natural Gas Swaps [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives		0	0
Cost of Sales [Member] | Derivatives designated as fair value hedges | Future [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives		345	0
Cost of Sales [Member] | Derivatives designated as fair value hedges | Call options
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	0	0	(81)
Cost of Sales [Member] | Derivatives designated as fair value hedges | Propane Swap Agreement
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	1,607	(364)	(120)
Inventories [Member] | Not Designated as Hedging Instrument [Member] | Natural Gas Swaps [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ 1	$ 0	$ 0