Derivative Instruments - Fair Values of Derivative Contracts Recorded in Condensed Consolidated Balance Sheet (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Energy Marketing Contract Liabilities, Current	$ 20	$ 1,018
Energy Marketing Contracts Assets, Current	46	1,055
Mark To Market Energy Assets [Member] | Forward Contracts [Member]
Derivatives, Fair Value [Line Items]
Energy Marketing Contracts Assets, Current	8	407
Mark To Market Energy Assets [Member] | Call options [Member]
Derivatives, Fair Value [Line Items]
Energy Marketing Contracts Assets, Current	0	26
Mark To Market Energy Assets [Member] | Put Option [Member]
Derivatives, Fair Value [Line Items]
Energy Marketing Contracts Assets, Current	38	622
Mark-to-market energy liabilities [Member] | Forward Contracts [Member]
Derivatives, Fair Value [Line Items]
Energy Marketing Contract Liabilities, Current	8	283
Mark-to-market energy liabilities [Member] | Propane Swap Agreement [Member]
Derivatives, Fair Value [Line Items]
Energy Marketing Contract Liabilities, Current	$ 12	$ 735