Derivative Instruments - Fair Values of Derivative Contracts Recorded in Condensed Consolidated Balance Sheet (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Derivatives, Fair Value [Line Items]
Document Period End Date	Sep. 30, 2014
Energy Marketing Contract Liabilities, Current	$ 141	$ 127
Energy Marketing Contracts Assets, Current	187	385
Mark To Market Energy Assets [Member] | Forward Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivatives asset not designated as hedging instruments, Forward contracts, Asset Derivatives	83	196
Mark To Market Energy Assets [Member] | Call options [Member]
Derivatives, Fair Value [Line Items]
Derivatives asset not designated as hedging instruments, Call Option, Derivatives assets	0	169
Cash Flow Hedge Derivative Instrument Assets at Fair Value	35
Mark To Market Energy Assets [Member] | Put Option [Member] | Derivatives designated as fair value hedges [Member]
Derivatives, Fair Value [Line Items]
Derivatives designated as fair value hedges, Asset derivatives	56	20
Mark To Market Energy Assets [Member] | Propane Swap Agreement [Member]
Derivatives, Fair Value [Line Items]
Cash Flow Hedge Derivative Instrument Assets at Fair Value	13
Mark-to-market energy liabilities [Member] | Forward Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivatives not designated as hedging instruments, Liability derivatives	81	127
Mark-to-market energy liabilities [Member] | Propane Swap Agreement [Member]
Derivatives, Fair Value [Line Items]
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value	$ 60