Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2012

Fair Value Disclosures [Abstract]

Assets and liabilities measured at fair value on a recurring basis

Assets and liabilities measured at fair value on a recurring basis are summarized below:

	Fair Value Measurements as of September 30, 2012
	Total		Level 1		Level 2		Level 3
	(in millions)
Cash and cash equivalents	$	399.1	$	399.1	$	—	$	—
Option contracts	0.3		—		—		0.3
Total assets	$	399.4	$	399.1	$	—	$	0.3
Basis swaps	$	0.3	$	—	$	—	$	0.3
Option contracts	0.2		—		—		0.2
Total liabilities	$	0.5	$	—	$	—	$	0.5

	Fair Value Measurements as of December 31, 2011
	Total		Level 1		Level 2		Level 3
	(in millions)
Cash and cash equivalents	$	343.3	$	343.3	$	—	$	—
Option contracts	1.0		—		—		1.0
Total assets	$	344.3	$	343.3	$	—	$	1.0
Option contracts	$	0.7	$	—	$	—	$	0.7
Total liabilities	$	0.7	$	—	$	—	$	0.7

Assets and liabilities measured at fair value on a recuring basis using significant unobservable inputs (level 3)

The following table presents the Company’s activity for assets and liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3):

	Fuel Derivative Activity for Three Months Ended September 30, 2012
	(in millions)
Balance at June 30, 2012	$	(1.0	)
Total gains (losses) realized or unrealized included in earnings, net	1.5
Settlements, net	(0.6		)
Balance at September 30, 2012	$	(0.1	)

	Fuel Derivative Activity for Nine Months Ended September 30, 2012
	(in millions)
Balance at December 31, 2011	$	0.3
Total gains (losses) realized or unrealized included in earnings, net	0.1
Settlements, net	(0.5		)
Balance at September 30, 2012	$	(0.1	)