Supplemental Information (Accounts Payable and Accrued Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Accounts Payable and Accrued Liabilities, Current [Abstract]
Accrued exploration and development costs	$ 109,939	$ 141,868
Accounts payable	86,051	99,444
Accrued interest	60,698	60,923
Accrued compensation	48,451	35,861
Accrued lease operating expenses	23,862	24,185
Taxes payable	27,523	13,455
Other	58,144	53,600
Total	$ 414,668	$ 429,336