Derivative Instruments - Fair Values of Derivative Contracts Recorded in Consolidated Balance Sheets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Derivative Asset Fair Value Net	$ 385	$ 210
Derivatives liability not designated as hedging instruments	127	331
Mark To Market Energy Assets | Forward Contracts
Derivatives, Fair Value [Line Items]
Derivatives asset not designated as hedging instruments	196	182
Mark To Market Energy Assets | Put Option
Derivatives, Fair Value [Line Items]
Derivative Asset Fair Value Net		0
Mark To Market Energy Assets | Put Option | Derivatives designated as fair value hedges
Derivatives, Fair Value [Line Items]
Derivative Asset Fair Value Net	20
Mark To Market Energy Assets | Call options
Derivatives, Fair Value [Line Items]
Derivatives asset not designated as hedging instruments		0
Mark To Market Energy Assets | Call options | Derivatives designated as fair value hedges
Derivatives, Fair Value [Line Items]
Derivative Asset Fair Value Net	0	28
Mark-to-market energy liabilities | Forward Contracts
Derivatives, Fair Value [Line Items]
Derivatives liability not designated as hedging instruments	$ 127	$ 331