Accounts Payable and Accrued Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Accounts Payable and Accrued Liabilities
Accounts payable	$ 63,955	$ 128,855
Accrued liabilities:
Accrued exploration, development and production	25,978	20,616
Accrued general and administrative expenses	11,173	5,089
Accrued taxes other than income	13,635	11,124
Accrued interest	248
Income taxes	20,778	4,192
Accrued liabilities	$ 71,812	$ 41,021