Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Significant Accounting Policies [Line Items]
(Gain) loss on fuel call options			$ (11,701,000)	$ 4,167,000
Taxes directly imposed on a revenue-producing transaction between a seller and a customer	$ 130,400,000	$ 120,000,000	$ 329,300,000	$ 295,400,000