Derivative instruments (Tables)

6 Months Ended

Jun. 30, 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 June 30, 2012		Fair Value at June 30, 2011		Fair Value at December 31, 2011
		(In thousands)
Designated as hedges:
Commodity derivatives	Commodity derivative instruments	$	36,360	$	14,040	$	27,687
	Other assets - noncurrent	11,445		6,265		2,768
		47,805		20,305		30,455
Not designated as hedges:
Commodity derivatives	Commodity derivative instruments	640		194		—
	Other assets - noncurrent	212		—		—
		852		194		—
Total asset derivatives		$	48,657	$	20,499	$	30,455

Liability Derivatives	Location on Consolidated Balance Sheets	Fair Value at June 30, 2012		Fair Value at June 30, 2011		Fair Value at December 31, 2011
		(In thousands)
Designated as hedges:
Commodity derivatives	Commodity derivative instruments	$	789	$	17,780	$	12,727
	Other liabilities - noncurrent	—		6,735		937
Interest rate derivatives	Other accrued liabilities	6,963		—		827
	Other liabilities - noncurrent	—		—		3,935
		7,752		24,515		18,426
Not designated as hedges:
Commodity derivatives	Commodity derivative instruments	248		906		437
	Other liabilities - noncurrent	—		—		—
		248		906		437
Total liability derivatives		$	8,000	$	25,421	$	18,863