Derivative instruments (Tables)

3 Months Ended

Mar. 31, 2012

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Derivative Instruments (Tables)

The location and fair value of the Company's derivative instruments in the Consolidated Balance Sheets were as follows:

Asset Derivatives	Location on Consolidated Balance Sheets	Fair Value at		Fair Value at		Fair Value at
		March 31, 2012		March 31, 2011		December 31, 2011
		(In thousands)
Designated as hedges:
Commodity derivatives	Commodity derivative instruments	$	25,560	$	13,250	$	27,687
	Other assets - noncurrent	537		3,148		2,768
		26,097		16,398		30,455
Not designated as hedges:
Commodity derivatives	Commodity derivative instruments	1,138		—		—
	Other assets - noncurrent	45		—		—
		1,183		—		—
Total asset derivatives		$	27,280	$	16,398	$	30,455

Liability Derivatives	Location on Consolidated Balance Sheets	Fair Value at		Fair Value at		Fair Value at
		March 31, 2012		March 31, 2011		December 31, 2011
		(In thousands)
Designated as hedges:
Commodity derivatives	Commodity derivative instruments	$	18,964	$	35,990	$	12,727
	Other liabilities - noncurrent	6,098		18,082		937
Interest rate derivatives	Other accrued liabilities	1,168		—		827
	Other liabilities - noncurrent	2,153		—		3,935
		28,383		54,072		18,426
Not designated as hedges:
Commodity derivatives	Commodity derivative instruments	1,219		4,509		437
	Other liabilities - noncurrent	49		—		—
		1,268		4,509		437
Total liability derivatives		$	29,651	$	58,581	$	18,863