Derivative Instruments - Additional Information (Detail) gal in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015 USD ($) Counterparty $ / gal gal	Dec. 31, 2014 USD ($) Counterparty $ / gal gal
Propane Swap Agreement [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | gal	2,500	630
Cash Paid On Derivative Settlement | $	$ 1,100,000
Other Comprehensive Income Loss Adjustments AOCI Swap Agreements | $		$ 735,000
Call options [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | gal		1,300
Payments for Derivative Instrument, Financing Activities | $		$ 98,000
Put Option [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | gal	2,500	630
Payments for Derivative Instrument, Financing Activities | $	$ 143,000	$ 128,000
Cash Received On Derivative Settlement | $	$ 868,000
Forward Contracts [Member]
Derivative [Line Items]
Number Of Counterparties With Master Repurchase Agreements | Counterparty	2	2
Accounts Receivable Subject To Master Netting Arrangement | $		$ 1,600,000
Accounts Payable Subject To Master Netting Arrangement | $		$ 1,200,000
Mark To Market Energy Liabilities [Member] | Propane Swap Agreement [Member]
Derivative [Line Items]
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value | $	$ 128,000
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 | $	$ 64,000
Strike Price 1 [Member] | Propane Swap Agreement [Member]
Derivative [Line Items]
Strike Price Per Gallon For The Propane Swap Agreements	0.595	1.1350
Strike Price 2 [Member] | Propane Swap Agreement [Member]
Derivative [Line Items]
Strike Price Per Gallon For The Propane Swap Agreements	0.5888	1.0975
Strike Price 3 [Member] | Propane Swap Agreement [Member]
Derivative [Line Items]
Strike Price Per Gallon For The Propane Swap Agreements	0.5500	1.0475
Strike Price 4 [Member] | Propane Swap Agreement [Member]
Derivative [Line Items]
Strike Price Per Gallon For The Propane Swap Agreements	0.5200
Put Option Strike Price 1 [Member] | Put Option [Member]
Derivative [Line Items]
Derivative, Price Risk Option Strike Price	0.4950	1.0350
Put Option Strike Price 2 [Member] | Put Option [Member]
Derivative [Line Items]
Derivative, Price Risk Option Strike Price	0.4888	0.9975
Put Option Strike Price 3 [Member] | Put Option [Member]
Derivative [Line Items]
Derivative, Price Risk Option Strike Price	0.4500	0.9475
Put Option Strike Price 4 [Member] | Put Option [Member]
Derivative [Line Items]
Derivative, Price Risk Option Strike Price	0.4200
Strike Price 1 [Member] | Call options [Member]
Derivative [Line Items]
Derivative, Price Risk Option Strike Price	1.0875
Strike Price 2 [Member] | Call options [Member]
Derivative [Line Items]
Derivative, Price Risk Option Strike Price	1.0650