Financial Derivative Instruments - Fuel Hedging (Details)	Sep. 30, 2013 gal
Remainder of 2013
Volume of Fuel Hedging [Line Items]
Fuel Hedged (in gallons)	208,000,000	[1]
2014
Volume of Fuel Hedging [Line Items]
Fuel Hedged (in gallons)	671,000,000	[1]
2015
Volume of Fuel Hedging [Line Items]
Fuel Hedged (in gallons)	790,000,000	[1]
2016
Volume of Fuel Hedging [Line Items]
Fuel Hedged (in gallons)	977,000,000	[1]
2017
Volume of Fuel Hedging [Line Items]
Fuel Hedged (in gallons)	933,000,000	[1]

[1] The Company determines gallons hedged based on market prices and forward curves as of September 30, 2013. Due to the types of derivatives utilized by the Company, these volumes may vary significantly as market prices fluctuate.