Fair Value (Tables)

6 Months Ended

Jun. 30, 2011

Fair Value

Carrying Amounts and Fair Values of Our Financial Instruments

Assets (Liabilities)	December 31, 2010						June 30, 2011
	Carrying Amount			Fair Value			Carrying Amount			Fair Value
Cash and cash equivalents	$	7,483		$	7,483		$	12,992		$	12,992
Restricted cash	$	14,379		$	14,379		$	—		$	—
Energy commodity derivatives deposits	$	22,302		$	22,302		$	43,505		$	43,505
Long-term receivables	$	1,167		$	1,161		$	1,710		$	1,705
Energy commodity derivatives contracts (current)	$	(11,790	)	$	(11,790	)	$	(8,180	)	$	(8,180	)
Energy commodity derivatives contracts (noncurrent)	$	(4,920	)	$	(4,920	)	$	(10,962	)	$	(10,962	)
Debt	$	(1,906,148	)	$	(2,048,895	)	$	(2,042,246	)	$	(2,247,520	)
Interest rate swaps (current)	$	—		$	—		$	2,678		$	2,678
Interest rate swaps (noncurrent)	$	—		$	—		$	1,849		$	1,849

Recurring Fair Value Measurements of Our Commodity Contracts and Interest Rate Swaps

Assets (Liabilities)				Fair Value Measurements as of December 31, 2010 using:
	Total			Quoted Prices in Active Markets for Identical Assets (Level 1)			Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Energy commodity derivatives contracts (current)	$	(11,790	)	$	(11,790	)	$	—	$	—
Energy commodity derivatives contracts (noncurrent)	$	(4,920	)	$	(4,920	)	$	—	$	—

Assets (Liabilities)				Fair Value Measurements as of June 30, 2011 using:
	Total			Quoted Prices in Active Markets for Identical Assets (Level 1)			Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Energy commodity derivatives contracts (current)	$	(8,180	)	$	(8,180	)	$	—	$	—
Energy commodity derivatives contracts (noncurrent)	$	(10,962	)	$	(10,962	)	$	—	$	—
Interest rate swaps (current)	$	2,678		$	—		$	2,678	$	—
Interest rate swaps (noncurrent)	$	1,849		$	—		$	1,849	$	—