Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2013

Fair Value Disclosures [Abstract]

Schedule of assets and liabilities measured at fair value on a recurring basis

The following table presents the Company's assets and liabilities that are measured at fair value as of March 31, 2013:

	Fair Value Measurement at the End of the Reporting Period Using
	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Fair Value at March 31, 2013
	(in thousands)
Recurring fair value measurements
Assets:
Trading securities	$	158	$	142	$	—	$	300
Commodity derivatives	—		246,552		—		246,552
Deferred compensation plan assets	53,768		—		—		53,768
Total assets	53,926		246,694		—		300,620
Liabilities:
Commodity derivatives	—		28,001		—		28,001
Interest rate derivatives	—		5,784		—		5,784
Total liabilities	—		33,785		—		33,785
Total recurring fair value measurements	$	53,926	$	212,909	$	—	$	266,835

Schedule of carrying values and financial instruments not carried at fair value

Carrying values and fair values of financial instruments that are not carried at fair value in the consolidated balance sheet as of March 31, 2013 and December 31, 2012 are as follows:

	March 31, 2013				December 31, 2012
	Carrying Value		Fair Value		Carrying Value		Fair Value
	(in thousands)
Long-term debt	$	3,017,280	$	3,768,884	$	3,721,193	$	4,555,770