Fair Value (Tables)

6 Months Ended

Jun. 30, 2012

Fair Value [Abstract]

Schedule Of Carrying Amounts And Fair Values Of Financial Instruments

		December 31, 2011						June 30, 2012
		Carrying			Fair			Carrying			Fair
Assets (Liabilities)		Amount			Value			Amount			Value
Cash and cash equivalents	$	209,620		$	209,620		$	233,716		$	233,716
Energy commodity derivatives deposits (current assets)	$	26,917		$	26,917		$	8,239		$	8,239
Energy commodity derivatives deposits (current liabilities)
	$	—		$	—		$	(17,196	)	$	(17,196	)
Long-term receivables	$	2,534		$	2,510		$	3,097		$	3,065
Energy commodity derivatives contracts (current assets)	$	4,914		$	4,914		$	13,878		$	13,878
Forward-starting interest rate swap agreements
(noncurrent)	$	—		$	—		$	1,008		$	1,008
Energy commodity derivatives contracts (noncurrent
liabilities)	$	(6,457	)	$	(6,457	)	$	(2,008	)	$	(2,008	)
Debt	$	(2,151,775	)	$	(2,389,700	)	$	(2,148,432	)	$	(2,426,955	)

Schedule Of Recurring Fair Value Measurements Of Commodity Contracts

					Fair Value Measurements as of
					December 31, 2011 using:
					Quoted Prices in			Significant
					Active Markets			Other		Significant
					for Identical			Observable		Unobservable
					Assets			Inputs		Inputs
Assets (Liabilities)		Total			(Level 1)			(Level 2)		(Level 3)
Long-term receivables	$	2,510		$	—		$	—	$	2,510
Energy commodity derivatives contracts (current assets)	$	4,914		$	4,914		$	—	$	—
Energy commodity derivatives contracts (noncurrent
liabilities)	$	(6,457	)	$	(6,457	)	$	—	$	—
Debt	$	(2,389,700	)	$	(2,389,700	)	$	—	$	—

					Fair Value Measurements as of
							June 30, 2012 using:
					Quoted Prices in			Significant
					Active Markets			Other		Significant
					for Identical			Observable		Unobservable
					Assets			Inputs		Inputs
Assets (Liabilities)		Total			(Level 1)			(Level 2)		(Level 3)
Long-term receivables	$	3,065		$	—		$	—	$	3,065
Energy commodity derivatives contracts (current assets)	$	13,878		$	13,878		$	—	$	—
Forward-starting interest rate swap agreements
(noncurrent)	$	1,008		$	—		$	1,008	$	—
Energy commodity derivatives contracts (noncurrent
liabilities)	$	(2,008	)	$	(2,008	)	$	—	$	—
Debt	$	(2,426,955	)	$	(2,426,955	)	$	—	$	—