Supplemental Disclosures to the Consolidated Statements of Cash Flows (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Net cash provided by operating activities included:
Cash payments for interest	$ 18,794	$ 16,787
Interest capitalized	(2,942)	(3,628)
Cash payments for interest, net of amounts capitalized	15,852	13,159
Non-cash investing activities included:
Asset retirement obligation additions and revisions	139	76
Oil and natural gas properties acquired through increase in accounts payable and accrued liabilities	$ 18,629	$ 18,502