Supplemental Disclosures to the Consolidated Statements of Cash Flows (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Net cash provided by operating activities included:
Cash payments for interest	$ 71,475	$ 72,366
Interest capitalized	(3,311)	(1,835)
Cash payments for interest, net of amounts capitalized	68,164	70,531
Cash (receipts) payments for income taxes	100	101
Non-cash investing activities included:
Asset retirement costs capitalized	551	396
Oil and natural gas properties acquired through increase (decrease) in accounts payable and accrued liabilities	$ 38,184	$ 10,301