Derivative Instruments (Tables)

3 Months Ended

Mar. 31, 2012

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Schedule of commodity derivatives

	2012	2013	2014
Oil Bbl/D:	21,000	15,000	4,000
Natural Gas MMBtu/D:	—	—	—

Schedule of crude oil three way collars entered

Term	Average Barrels Per Day	Sold Put / Purchased Put / Sold Call
Full year 2014	1,000	$70.00 / $90.00 / $120.00
Full year 2014	1,000	$70.00 / $90.00 / $121.80

Schedule of derivative assets and liabilities

	March 31, 2012
	Derivative Assets			Derivative Liabilities
(in millions)	Balance Sheet Classification	Fair Value		Balance Sheet Classification	Fair Value
Current:
Commodity	Derivative assets	$	0.3	Derivative liabilities	$	44.7
Long term:
Commodity	Derivative assets	0.3		Derivative liabilities	19.3
Total derivatives		$	0.6		$	64.0

	December 31, 2011
	Derivative Assets			Derivative Liabilities
(in millions)	Balance Sheet Classification	Fair Value		Balance Sheet Classification	Fair Value
Current:
Commodity	Derivative assets	$	6.1	Derivative liabilities	$	20.4
Long term:
Commodity	Derivative assets	7.0		Derivative liabilities	15.5
Total derivatives		$	13.1		$	35.9

Summary of (gains) losses before income taxes of derivative instruments recognized in the condensed statements of income (loss)

		Three Months Ended March 31,
(in millions)	Location of (Gain) Loss Recognized in Earnings
Description of (Gain) Loss		2012			2011
Commodity
Loss reclassified from AOCL into earnings (amortization of frozen amounts)	Sales of oil and natural gas	$	2.7		$	14.6
Loss recognized in earnings (cash settlements and mark-to-market movements)	Realized and unrealized loss on derivatives, net	28.5			127.5
Interest rate
(Gain) loss reclassified from AOCL into earnings (amortization of frozen amounts)	Interest	$	(0.6	)	$	0.8