Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2011

Fair Value Measurements [Abstract]

Fair Value Hierarchy Table for Assets and Liabilities Measured at Fair Value

	Fair Value Measurements at September 30, 2011 Using:
	Quoted Prices in		Significant					Total
	Active Markets		Other			Significant		Carrying
	for Identical		Observable			Unobservable		Value as of
	Assets		Inputs			Inputs		September 30,
	(Level 1)		(Level 2)			(Level 3)		2011
Trading securities held in our deferred compensation plans	$	49,199	$	—		$	—	$	49,199
Derivatives — swaps		—		56,185			—		56,185
— collars		—		148,161			—		148,161
— call options		—		(20,737	)		—		(20,737	)

Values of assets measured at fair value on nonrecurring basis

	Three Months Ended September 30,								Nine Months Ended September 30,
	2011				2010				2011				2010
	Fair				Fair				Fair				Fair
	Value		Impairment		Value		Impairment		Value		Impairment		Value		Impairment
Natural gas and oil properties	$	24,388	$	38,681	$	—	$	—	$	24,388	$	38,681	$	16,075	$	6,505

Carrying Amounts and Fair Values of Financial Instruments

	September 30, 2011						December 31, 2010
	Carrying			Fair			Carrying			Fair
	Value			Value			Value			Value
Assets:
Commodity swaps, collars, call options and basis swaps	$	183,609		$	183,609		$	123,255		$	123,255
Commodity collars — discontinued operations		—			—			8,195			8,195
Marketable securities(a)		49,199			49,199			47,794			47,794
Liabilities:
Commodity swaps, collars, call options and basis swaps		—			—			(13,764	)		(13,764	)
Bank credit facility(b)		—			—			(274,000	)		(274,000	)
6.375% senior subordinated notes due 2015(b)		—			—			(150,000	)		(153,000	)
7.5% senior subordinated notes due 2016(b)		—			—			(249,683	)		(259,375	)
7.5% senior subordinated notes due 2017(b)		(250,000	)		(265,000	)		(250,000	)		(263,438	)
7.25% senior subordinated notes due 2018(b)		(250,000	)		(266,250	)		(250,000	)		(263,750	)
8.0% senior subordinated notes due 2019(b)		(287,678	)		(328,500	)		(286,853	)		(326,625	)
6.75% senior subordinated notes due 2020(b)		(500,000	)		(532,500	)		(500,000	)		(515,625	)
5.75% senior subordinated notes due 2021(b)		(500,000	)		(518,750	)		—			—

(a)	Marketable securities are held in our deferred compensation plans.
(b)	The book value of our bank debt approximates fair value because of its floating rate structure. The fair value of our senior subordinated notes is based on end of period market quotes.