Derivative Instruments - Fair Values of Derivative Contracts Recorded in Condensed Consolidated Balance Sheet (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013		Jun. 30, 2013		Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Derivatives asset not designated as hedging instruments, Call Option, Derivatives assets			$ 102
Derivatives designated as fair value hedges, Asset derivatives	379				210
Derivatives not designated as hedging instruments, Liability derivatives	124				331
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	214				182
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	102				0
Mark-to-market energy assets [Member] | Call options [Member] | Derivatives designated as fair value hedges [Member]
Derivatives, Fair Value [Line Items]
Derivatives designated as fair value hedges, Asset derivatives	0	[1]			28	[1]
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	63	[2]	63	[2]	0	[2]
Mark-to-market energy liabilities [Member] | Forward Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivatives not designated as hedging instruments, Liability derivatives	$ 124				$ 331

[1] We purchased call options for the propane price cap program in May 2012. The call options expired in March 2013.

[2] As a fair value hedge with no ineffective portion, the unrealized gains and losses associated with these put options are recorded in cost of sales, offset by the corresponding change in the value of propane inventory (hedged item), which is also recorded in cost of sales. The amounts in cost of sales offset to zero and the unrealized gains and losses of this call option effectively changed the value of propane inventory.