Net Change in Operating Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		46 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012
Decrease (increase) in operating assets:
Accounts receivable	$ 25,408	$ (1,160)	$ (44,368)
Inventory	(4,442)	(1,175)	(82,654)
Prepaid expenses and other assets	382	(874)	(7,004)
Increase (decrease) in operating liabilities:
Accounts payable	(13,924)	2,803	6,494
Prepaid income taxes	1,560		(16,272)
Asset retirement obligation		(165)	(2,049)
Accrued expenses	(4,605)	2,074	8,032
Net change in operating assets and liabilities	$ 4,379	$ 1,503	$ (137,821)