Accounts Payable and Accrued Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Accounts Payable and Accrued Liabilities
Accounts payable	$ 128,855	$ 278,006
Accrued liabilities:
Accrued exploration, development and production	20,616	27,666
Accrued general and administrative expenses	5,089	2,159
Accrued taxes other than income	11,124	1,095
Accrued interest		1,208
Income taxes	4,192	5,066
Accrued liabilities	$ 41,021	$ 37,194